j^a^^tt^fe^^^^ia^ 


Presented  by 
Dain  L  Tasker,   D.   0, 


COLLEGE  OF  OSTEOPATHIC  PHYSICIANS 
AND  SURGEONS  •  LOS  ANGELES,  CALIFORNIA 


me. 


/  o  - 


THE  ANATOMY 

OF  THE 

CENTRAL  NERVOUS  SYSTEM 
OF  MAN 

AND    OF 

VERTEBRATES  IN  GENERAL. 
\3 

Prof.  LUDWIG  EDINGER,  M.D., 


FRANKFOHT-ON-THE-MAIN 


TRANSLATED    FROM    THE   FIFTH    GERMAN    EDITION 

BY 

WINFIELD  S.  HALL,  PH.D.,  M.D., 

PROFESSOR  OF  PHYSIOLOGY  IN  THE  NORTHWESTERN-  UNIVERSITY  MEDICAL  SCHOOL,  CHICAGO. 
ASSISTED  BY 

PHILO  LEON    HOLLAND,   M.D., 

INSTRUCTOR  IN  CLINICAL  NEUROLOGY  IN  THE  NORTHWESTERN  UNIVERSITY 
MEDICAL  SCHOOL,  CHICAGO, 


EDWARD   P.   CARLTON,   B.S., 

DEMONSTRATOR  OF  HISTOLOGIC  NEUROLOGY  IN  THE  NORTHWESTERN  UNIVERSITY  MEDICAL  SCHOOL,  CHICA 


Illustrated  with  25$  engravings. 


PHILADELPHIA,  NEW  YORK,  CHICAGO  : 
THE  F.  A.  DAVIS  COMPANY,  PUBLISHERS. 

1899. 


WLlo 


COPYRIGHT,  1899, 

THE  F.  A.  DAVIS  COMPANY. 

.[Registered  at  Stationers'  Hall,  London,  Eng.] 


Philadelphia,  Pa.,  U.  S.  A. 

The  Medical  Bulletin  Printing-House, 

1916  Cherry  Street. 


TO   HIS  TEACHER, 

PROFESSOR  WILHELM  WALDEYER, 

THIS  FIRST  ATTEMPT 

AT   A 

Comparative  Anatomy  of  the  Brain 

IS 

DEDICATED 
REVERENCE   AND  GRATITUDE. 

THE  AUTHOR. 


AUTHOR'S   PREFACE   TO    THE   FIFTH   GERMAN   EDITION. 


XOT  without  a  certain  hesitation  does  the  author  come  with  this  edition 
before  his  circle  of  readers.  Though  the  previously  small  book  has  now 
grown  to  larger  proportions,  still  it  presents  a  subject  which  has  not  pre- 
viously been  comprehensively  treated:  the  comparative  morphology  of  the 
central  nervous  system. 

Three  parts  have  arisen  from  the  original  little  work:  parts  which 
are  so  far  independent  of  each  other  that  they  who  have  less  interest 
for  the  more  general  matters  and  for  comparative  anatomy,  by  turning 
past  the  first  two  parts  will  find  in  the  third  a  somewhat  enlarged  and 
richly-illustrated  edition  of  the  old  book.  Grateful  for  the  interest  which 
the  medical  profession  have  manifested  in  the  work,  the  third  part,  which 
deals  exclusively  with  the  mammalian,  and  especially  with  the  human,  brain, 
has  been  carefully  rewritten  and  enlarged  through  the  addition  of  numerous 
figures  made  from  photographs  of  sections.  In  order  to  facilitate  the  study 
from  sections  a  complete  series  of  frontal  sections  through  the  entire  brain 
has  been  added. 

Part  I  is  introductory,  giving  the  fundamental  ideas  accepted  at  the 
present  time.  It  takes  into  consideration  also  function,  which  was  not  con- 
sidered in  earlier  editions. 

The  second  part  of  the  book  realizes  finally  a  plan  which,  since  the  be- 
ginning of  my  studies  in  brain-anatomy,  I  have  never  allowed  to  escape  my 
eye.  Resting  almost  completely  upon  my  own  investigations,  it  gives  a 
review  of  that  which  may  be  said,  with  some  certainty,  of  the  structure  and 
course  of  development  of  the  central  nervous  system  in  the  vertebrate  series. 
Those  who  have  worked  in  this  field,  still  cultivated,  will,  considering  the 
difficulties  which  tower  up  everywhere,  leniently  judge  that  which  is  prof- 
fered. The  first  attempt  at  a  general  presentation,  the  book  shows  every- 
where the  insufficiencies  which  such  a  work  must  present.  No  one  knows 
that  better  than  the  author  himself.  If,  as  here,  the  plan  of  the  whole 
forbids  going  into  details,  it  will  not  be  possible  to  always  give  a  sufficient 
foundation  for  that  which  is  presented.  So  far  as  it  has  been  possible,  this 
has  been  supplied  in  the  numerous  figures  whose  addition  has  been  made 
possible  through  the  liberality  of  the  publishers.  This  edition  contains  113 
figures  more  than  the  Fourth,  and  of  the  new  ones,  99  are  devoted  to  com- 
parative anatomy.  The  central  nervous  system  has  formerly  been  studied 


vi  AUTHOR'S  PREFACE  TO  THE  FIFTH  GERMAN  EDITION. 

mostly  by  physicians.  To  them,  naturally,  the  first  task  was  to  gain  a 
better  understanding  of  the  human  brain,  only  the  mammalian  brain  being 
brought  in  for  comparison.  We  possess,  however,  even  of  the  lower  verte- 
brate types,  several  excellent  descriptions. 

By  comparing  animals  low  down  in  the  vertebrate  series  the  attempt 
is  here  made  to  determine  where  particular  structures  appear,  how  they  vary, 
and  what  functions  they  may  perform  at  different  stages  of  their  develop- 
ment. It  has  also  been  attempted  to  determine  what  belongs  to  each 
separate  part  of  the  nervous  system  as  essential  and  fundamental.  It  is  an 
attempt  in  which  the  author  believed  himself  justified,  in  view  of  the  fact 
that  he  had  been  occupied  ten  years  in  studies  in  the  realm  of  comparative 
neurology. 

The  preface  to  the  second  edition  of  this  book  closed  with  the  following 
words:  "There  must  be  a  number  of  anatomical  mechanisms  which  are  alike 
present  in  all  vertebrates:  those  which  make  possible  the  simplest  expres- 
sions of  the  activity  of  the  central  nervous  system.  It  is  only  necessary  to 
find  that  animal,  or  that  stage  of  development  of  any  animal,  in  which  this 
or  that  mechanism  appears  in  so  simple  a  form  that  it  may  be  completely 
understood.  Once  one  has  anywhere  perfectly  established  the  relation  of 
such  a  mechanism — e.g.,  a  nerve-bundle  or  a  cellular  structure — he  is  usually 
able  to  readily  find  it  again  even  where,  through  adventitious  matter,  it  is 
made  more  or  less  obscure.  The  discovery  of  such  fundamental  features  of 
brain-structure  appears  to  be  the  next  and  most  important  task  of  brain- 
morphology.  Once  we  know  them,  it  will  be  easier  to  understand  the  com- 
plicated mechanisms  with  which  the  more  highly  organized  brain  performs 
its  function." 

This  was,  in  a  way,  a  programme  which  has,  in  part,  been  carried  out  in 
the  new  edition. 

EDINGER. 
FRANKFURT-AM-MAIX,  JUNE.  1896. 


TRANSLATOR'S   PREFACE. 


THE  hearty  reception  accorded  by  the  medical  students  and  practi- 
tioners of  America  to  Professor  Riggs's  translations  of  the  earlier  German 
editions  makes  it  unnecessary  for  the  editor  of  the  present  translation  to 
introduce  the  work  to  Professor  Edinger's  circle  of  American  readers. 

The  additions  which  have  been  made  to  the  original  since  the  last 
English  translation  increases  the  range  of  its  usefulness.  Originally  ad- 
dressed particularly  to  the  needs  of  the  medical  profession,  it  now  contains 
matter  which  is  practically  indispensable  to  the  general  student  of  neurology 
or  of  physiological  psychology  in  the  biological  departments  of  our  universi- 
ties. 

In  a  few  instances  passages,  in  Part  II  of  the  original,  which  appear  in 
fine  print  and  serve  to  amplify  or  to  further  explain  certain  statements  of 
the  text,  have  been  condensed  or  omitted,  justification  for  this  being  urged 
in  the  somewhat  different  needs  of  the  American  readers  of  the  work.  The 
"lectures"  of  the  original  have  been  presented  as  Chapters.  This  necessitates 
an  occasional  departure  from  the  diction  of  the  original. 

The  translators  take  this  opportunity  to  acknowledge  the  efficient 
assistance  of  Mr.  J.  C.  Gordon,  of  the  Wisconsin  State  University,  in  the 
preparation  of  the  manuscript. 

The  fullness  of  the  index  prepared  by  Dr.  Charles  L.  Mix,  Instructor 
in  Neurology  in  the  Northwestern  University  Medical  School,  adds  much 
to  the  value  of  the  book,  both  in  its  use  as  a  text-book  and  as  a  book  for 
reference.  The  translators  express  herewith  their  appreciation  of  the  work 
done  by  Dr.  Mix  in  preparing  the  index,  and  also  in  making  the  final  proof- 
reading. 

WIXFIELD  S.  HALL. 
CHICAGO,  NOVEMBER,  1898. 


(vii) 


TABLE  OF  CONTENTS. 


PAET  I. 

INTRODUCTION  TO  THE  ANATOMY  OF  THE  CENTRAL  NERVOUS  SYSTEM. 

CHAPTER  I.  PAGE 

Review    of    the    History    and    the    Methods    of    Investigation    of    the    Central 

Nervous  System 3 

CHAPTER  II. 
Fundamental  Conceptions:    Ganglion-cell  and  Nerve 15 

CHAPTER  III. 
Central  Organ  and  Peripheral  Nerves   (Physiological) 31 


PAET  II. 

REVIEW  OF  THE  EMBRYOLOGY  AND  THE  COMPARATIVE  ANATOMY  OF 
THE  VERTEBRATE  BRAIN. 

CHAPTER  IV. 
The  Development  of  the  Brain  and  of  Ganglia 47 

CHAPTER  V. 
The  Structure  of  the  Spinal  Cord 62 

CHAPTER  VI. 
The  Oblongata  and  the  Nuclei  of  the  Cranial  Nerves 75 

CHAPTER  VII. 
The  Medulla  Oblongata :    Epencephalon  ( Continued) 91 

CHAPTER  VIII. 

The  Cerebellum:    Metencephalon 101 

(ix) 


X  TABLE    OF    CONTENTS. 

CHAPTER  IX.                                                        PAGK 
The  Midbrain,  or  Mesencephalon 112 

CHAPTER  X. 
The  Thalamus :    Thalamencephalon  or  Interbrain 125 

f  CHAPTER  XI. 

The  Cerebrum:    Prosencephalon  or  Forebrain.     I.  The  Olfactory  Apparatus.     II. 

The  Corpus  Striatum 145 

CHAPTER  XII. 
The  Cerebrum  (Continued) .    III.  The  Brain-mantle 159 


PAET  III. 

THE  SPECIAL  ANATOMY  OF  THE  MAMMALIAN  BRAIN,  WITH  SPECIAL 
CONSIDERATION  OF  THE  HUMAN  BRAIN. 

CHAPTER  XIII. 

The  Form-relations  of  the  Human  Brain ...  .    1  i 


CHAPTER  XIV. 
The  Brain  of  Mammals  and  the  Olfactory  Apparatus 208 

CHAPTER  XV. 

The  Cortex  of  the  Forebrain  and  the  Medulla  of  the  Hemispheres;    the  Com- 
missures and  the  Corona  Radiata 227 

CHAPTER  XVI. 
The  Capsula  Interna,  the  Corpus  Striatum,  and  the  Ganglia  of  the  Interbrain ....   248 

CHAPTER  XVII. 

The  Metathalamus  and  Hypothalamus.    The  Regio  Subthalamica  and  the  Struct- 
ures at  the  Base  of  the  Brain 271 

CHAPTER  XVIII. 

The  Base  of  the  Brain.     The  Optic  Nerve  and  its  Origin.     The  Corpora  Quadri- 

gemina 280 


TABLE    OF    CONTENTS.  XI 

CHAPTER  XIX.                                                          PAGE 
The  Tegmentum  and  the  Peduncle  of  the  Midbrain 295 

CHAPTER  XX. 
The  Pons  and  the  Cerebellum 310 

CHAPTER  XXI. 

The  Peripheral  Nerve-roots,  the  Spinal  Ganglia,  and  the  Spinal  Cord 332 

CHAPTER  XXII. 
The  Course  of  the  Fibers  in  the  Spinal  Cord 351 

CHAPTER  XXIII. 
The  Medulla  Oblongata 363 

CHAPTER  XXIV. 
The  Medulla  Oblongata  and  the  Tegmentum  of  the  Pons 379 

CHAPTER  XXV. 
Final  Review 401 

INDEXES. 

Index  of  Authors 411 

Index  of  Comparative  Neurology 413 

•General  Index .  .   423 


PART  I. 


INTRODUCTION  TO  THE  ANATOMY  OF  THE 
CENTRAL  NERVOUS  SYSTEM. 


(1) 


CHAPTER    I. 

BE  VIEW  OF  THE  HISTORY  AND  THE  METHODS  OF  INVESTIGATION  OF 
THE  CENTRAL  NERVOUS  SYSTEM. 

THE  anatomy  of  the  central  nervous  system,  whose  features  these 
chapters  are  to  present,  has,  since  the  renaissance  of  anatomy,  engaged  the 
lively  interest  of  numerous  investigators.  Vesalius,  Eustachio  Aranzio, 
Yariolo,  and  Fallopia  laid  the  foundations  upon  which,  in  subsequent 
centuries,  the  superstructure  could  be  built.  Even  in  the  seventeenth 
century  there  appeared  extensive  monographs,  which,  considering  the  tech- 
nique at  command  at  that  time,  must  be  recognized  as  practically  exhaust- 
ive: e.g.,  the  books  of  Th.  Willis  and  of  Eaim,  Vieussens.  Nevertheless 
Willis  could  still  describe  as  new  such  structures  as  the  corpus  striatum,  the 
anterior  commissure,  the  pyramids,  and  the  olivary  bodies.  Important  con- 
tributions on  brain-anatomy  were  made  even  at  that  time  by  Sylvius, 
Wepfer,  and  Van  Leeuwenhoek,  the  last  of  whom  was  first  to  make  a 
microscopic  investigation  of  the  brain.  Malacarne,  in  Italy;  von  Soemmer- 
ing,  in  Germany;  Vicq  d'Azyr  and  Eolando,  in  France,  contributed  much, 
in  the  latter  part  of  the  eighteenth  century,  to  the  extension  of  our  knowl- 
edge of  the  brain. 

As  our  century  dawned  there  was  scarcely  anything  of  importance  to 
be  added  to  the  gross  anatomy  of  the  organs  of  the  central  nervous  system. 
Little  progress  had  been  made,  however,  in  what  we  must  now  recognize 
as  the  most  important  part  of  the  morphology  of  the  central  nervous  system, 
namely:  in  the  knowledge  of  the  finer  relations  of  the  parts, — of  the  course 
of  the  fibers.  Even  investigations  in  the  comparative  anatomy  which  were 
made  in  the  first  decades  of  the  nineteenth  century  made  no  advance  in 
this  field.  What  remained  to  be  done  by  essentially  macroscopic  methods 
has  been  accomplished  by  Eeil,  Gall  and  Spurzheim,  Arnold,  Reichert, 
Foville,  Burdach,  et  al. 

Reil,  in  particular,  who  first  brought  into  general  recognition  as  a 
preparatory  method  the  artificial  hardening  of  the  brain,  had  discovered 
a  great  many  facts  which  do  not  appear  upon  the  surface. 

As  his  most  important  discovery  one  must  designate  the  boundary  of 
the  corona  radiata  and  the  pedunculi  cerebri,  whose  relation  to  the  corpus 
callosum,  which  traverses  them,  he  first  recognized;  the  Tractus  tecto- 
spinalis  and  its  origin  in  the  Corpora  Quadrigemina,  the  Nucleus  lenti- 

(3) 


4  ANATOMY    OF   THE    CENTEAL    NERVOUS    SYSTEM. 

formis,  the  insula,  and  many  other  structures  were  incorporated  into 
anatomy  only  after  his  investigations. 

As  a  landmark  at  the  beginning  of  this  earlier  period  stands  Burdach's 
book, — "On  the  Structure  and  Life  of  the  Brain," — in  which,  appearing 
in  1819,  the  author  had  carefully  collected  everything  which  had  been 
accomplished  up  to  that  time  and  added  much  explanatory  matter. 

Up  to  about  the  middle  of  this  century  the  technique  consisted,  for 
the  most  part,  of  gross  dissection  with  the  knife  and  of  the  separation  of 
the  fibers  of  hardened  pieces  of  brain-tissue  with  the  forceps.  Gall,  Bur- 
dach,  Eeil,  Arnold,  and  Foville  discovered  much  with  the  use  of  such 
methods. 

It  is  especially  due  to  Tiedemann  and  Reichert  that,  through  embry- 
ology, the  general  morphological  relations  came  to  be  better  understood. 

But  since  Ehrenberg  (1833)  had  demonstrated  that  the  brain  (Seelen- 
organ)  is  composed  of  innumerable  very  fine  tubes,  since  Eemak  (1838)  had 
described  the  ganglion-cells  more  exactly,  and  Hannover  (1840)  had 
demonstrated  their  connection  with  the  nerve-fibers,  it  was  clear  that  a 
simple  dissection  of  the  brain  and  cord  was  not  sufficient  to  yield  the 
desired  insight  inco  their  structure  and  relations. 

Stilling's  great  contribution  was  the  introduction  and  use  of  a  new 
method:  the  preparation  of  thin  sections,  or,  rather,  serial  sections,  which 
were  made  in  different,  but  definite,  directions  through  the  organ.1 

The  preparations  so  made  were  carefully  studied,  their  pictures  com- 
bined, and  thus  the  architecture  of  the  central  nervous  system  was  recon- 
structed. Through  these  methods  and  through  the  studies  which  he  made 
with  their  help,  Stilling  laid  the  foundations  for  the  modern  anatomy  of 
the  spinal  cord,  the  medulla,  the  pons,  and  the  cerebellum.  On  January 
25,  1842,  Stilling  allowed  a  piece  of  cord  to  freeze  in  a  temperature  of 
— 16°  C.  (3°  F.),  and  then  made,  with  a  scalpel,  a  fairly-thin  cross-section 
of  the  same.  "When  I  brought  this  under  the  microscope,"  he  writes,  "and 
with  15-diameters'  magnification  beheld  the  transverse  commissural  fibers, 
I  was  conscious  of  having  found  a  key  which  unlocked  the  secrets  of  the 
wonderful  structure  of  the  spinal  cord.  Archimedes  did  not  more  joyfully 
shout  'Eureka'  than  did  I  at  that  sight." 

Stilling's  method  is  the  one  still  most  used  for  the  study  of  the  central 
nervous  system.  Its  application  is  much  facilitated  by  the  hardening  of 
the  nervous  tissue  through  dilute  chromic  acid  or  solution  of  chrome-salts: 
a  procedure  introduced  by  Hannover  and  Eckhard.  The  sections  are 


1  Rolando  had  previously  made  thin  sections  of  the  central  nervous  system 
(1824),  but  the  reconstruction  of  the  organs  through  combinations  of  extended 
series  of  sections  is  due  particularly  to  Stilling. 


HISTORY   AND    METHODS    OF    INVESTIGATION.  5 

made  mostly  with  the  microtome,  which  makes  possible  exact  sectioning 
and  large  sections  of  unvarying  thickness.  Faultless  serial  sections  of  an 
entire  human  brain  can  now  be  prepared  less  than  1/20  millimetre  in 
thickness. 

The  sections  may  be  studied  unstained.  All  that  Stilling  found  was 
seen  in  such  unstained  preparations.  It  is  advisable,  however,  to  stain  them. 
We  are  indebted  to  Gerlach  (1858)  for  having  first  drawn  attention  to  the 
advantage  to  be  gained  through  a  soaking  of  the  preparation  in  carmin. 
Later  times  have  produced  many  staining  methods;  especially  have  anilin 
stains  (nigrosin,  etc.)  been  used.  But  only  recently  have  we,  through  Golgi 
(1883),  found  a  method  which  accomplishes  more  than  the  old  one  of  Ger- 
lach. This  method  is  based  upon  the  action  of  chrome-silver:  blackening 
the  cells  and  their  processes.  To  it  we  are  indebted  for  an  entirely  new 
and  unexpected  insight  into  the  finer  structure  of  the  central  nervous 
system. 

N~issl  first  made  it  possible,  through  careful  hardening  and  after- 
treatment  with  anilin  stains,  to  make  preparations  which  furnished  a 
glimpse  into  the  structure  of  a  ganglion-cell.  The  course  of  fibers  is  not 
made  much  plainer  through  carmin  staining.  On  the  other  hand,  it  is 
possible,  through  Weigert's  (1884)  valuable  method  of  haematoxylin  stain- 
ing, to  stain  even  the  finest  fibers  a  deep  blue-black,  and  so,  following  Still- 
ing's  method,  trace  their  course  more  easily  than  was  formerly  possible. 
One  may  also  get  beautiful  preparations  through  treatment  of  the  tissue 
with  osmic  acid,  following  Exner  and  Bellonci. 

Since  the  time  of  Clarke's  recommendations  on  this  point  (1851),  the 
stained  sections  are  dehydrated  in  alcohol  and  then  through  an  ethereal 
oil  or  through  xylol  made  transparent  ("cleared"). 

In  1886  Ehrlich  showed  that  it  is  possible,  with  methyl-blue,  to  stain 
axis-cylinders  and  ganglion-cells  of  living  animals.  In  the  hands  of  Eetzius 
and  others  this  process  has  become  of  the  greatest  importance  for  the  in- 
vestigation of  the  finer  structure  of  these  portions  of  the  central  nervous 
system. 

Most  of  the  investigators  who  have  worked  upon  the  central  nervous 
system  during  the  second  half  of  this  century  have  followed  Stilling's 
methods. 

We  are  indebted  to  two  men,  Stilling  and  Meynert,  for  most  that  we 
know  of  the  minute  structure  of  the  brain  and  cord.  It  is  to  be  noted 
that  all  later  investigators  have  proceeded  from  that  which  these  men 
established. 

Benedict  Stilling  laid  the  foundation  of  all  our  knowledge  of  the  pons, 
the  cerebellum,  the  medulla,  and  the  spinal  cord  through  a  series  of  most 
important  works  bearing  testimony  to  unapproached  industry:  works  which 


6  ANATOMY   OF   THE    CENTRAL   NERVOUS    SYSTEM. 

are  certain  to  make  for  the  great  Cassel  physician  a  monumentum  cere 
perennius. 

Meynert,  however,  not  only  systematically  worked  through  the  whole 
field  of  brain-  and  cord-  anatomy,  discovering,  through  sections  and  dis- 
sections, more  new  facts  than  had  any  previous  investigator,  Stilling  ex- 
cepted;  but,  upon  minute  anatomy  as  a  basis,  he  formulated  a  theory  of 
brain-structure  which  has  equally  influenced  anatomy  and  psychology,  bear- 
ing fruit  up  to  the  present  time  and  stimulating  investigators  to  new 
discoveries. 

From  the  nature  of  the  Stilling  method  it  follows  that  the  tracing  of 
a  nerve-tract  for  considerable  distances  is  made  certain  only  so  long  as  the 
elements  which  combine  to  form  it  are  not  interrupted  by  ganglion-cells 
or  turn  out  of  the  plane  of  the  section,  so  long  as  it  does  not  pass  into  a 
fiber  mesh-work  or  from  one  bundle  split  up  into  numerous  diverged 
fibrillse.  Even  in  the  spinal  cord  of  the  smallest  animals  it  seldom  occurs 
that  the  entire  course  of  a  fiber  may  be  seen  in  the  plane  of  one  section. 

It  was,  therefore,  necessary,  after  getting  one's  bearings  in  this  difficult 
field  through  Stilling's  work,  to  seek  for  further  methods  which  would  per- 
mit the  finding  and  tracing  of  nerve-tracts. 

As  is  well  known,  Waller  (1852)  showed  that  severed  nerves  de- 
generate in  a  definite  direction.  Tiirck  had  already  shown  (1850)  that  even 
the  interruption  of  conduction  in  the  spinal  cord  leads  to  degeneration, 
which  progresses  upward  in  some  tracts  and  downward  in  others. 

Through  his  studies,  as  well  as  through  those  of  Bouchard,  Flechsig, 
Charcot,  et  al,  it  was  successfully  demonstrated  that  in  definite  tracts  of 
the  spinal  cord  and  the  brain  lie  fibers  which,  when  degenerated,  separate 
themselves  from  the  normal  tissues  along  their  entire  course,  and  may 
thus  be  easily  followed.  The  study  of  these  secondary  degenerations  has 
since  become  important  for  the  advance  of  the  science  with  which  we 
are  employed.  For  this  reason  let  us  for  a  moment  discuss  Waller's  law 
somewhat  more  in  detail. 

It  is  now  formulated  as  follows:  The  axis-cylinder  of  a  nerve- fiber 
remains  intact  only  so  long  as  it  is  in  connection  with  its  parent-cell.  It 
degenerates  along  with  its  sheath  beyond  the  point  where  its  connection 
with  the  parent-cell  is  severed.  But  Forel  has  shown  that,  in  the  newborn 
after  simple  severing  of  the  nerve  and  in  adults  if  the  nerve  is  divided 
very  near  to  the  nucleus  (ganglion-cell),  degeneration  may  occur  also  in 
the  nerve-segment  which  is  connected  with  the  cell.  Bregmann  has  also,  in 
an  investigation  especially  planned  with  this  point  in  view,  confirmed  the 
theory  of  the  degeneration  of  the  central  stump.  This  apparent  contra- 
diction of  Waller's  law  has  been  solved  by  the  studies  of  Nissl.  Nissl  has 
shown  that  a  harmful  influence  is  exerted  upon  the  central  cell  from  the 


HISTORY   AND    METHODS    OF    INVESTIGATION.  7 

point  where  the  nerve  is  severed,  and  that  the  cell  may  be  temporarily 
much  damaged,  at  any  rate  structurally  modified.  In  such  cases  the  de- 
generation of  the  central  segment  of  the  axis-cylinder  also  supervenes, 
simply  because  it  is  not  in  connection  with  a  normal  parent-cell.  In  the 
consideration  of  secondary  degenerations  one  must,  in  future,  give  due 
weight  to  these  facts,  which  are  of  especial  importance  pathologically. 

The  region  through  which  such  a  degeneration  is  always  propagated 
is  called  a  tract  (Fasersystem).  A  number  of  diseases  of  the  spinal  cord, 
either  in  their  inception  or  throughout  their  course,  affect  particular  tracts: 
e.g.,  only  the  posterior  tracts  of  the  spinal  cord.  Such  diseases  are  called 
"System-diseases."  The  study  of  such  diseases  can  be  utilized  for  the 
increase  of  our  knowledge  of  the  course  of  nerve-tracts  (Flechsig,  Westphal, 
Striimpell).  Further,  through  an  exact  study  of  pathological  changes 
Charcot  and  his  pupils — especially  Pitres,  Fere,'  Bellet,  Brissaud,  et  al — 
have  added  much  to  our  knowledge  of  brain-anatomy. 

Occasionally  malformations  make  it  possible  to  differentiate  one  tract 
from  another  more  readily  than  in  the  normal  brain.  Thus  Kaufmann 
and  others  were  able  to  study  cases  of  absence  of  the  corpus  callosum  in 
which,  just  because  of  the  absence  of  the  commissure  in  question,  other 
features  of  the  brain  came  out  into  previously  unknown  prominence.  These 
observations  suggested  the  experimental  severing  of  particular  parts  of 
the  roots  or  of  the  spinal  cord,  and,  through  the  intentionally  induced 
secondary  degeneration,  to  gain  further  knowledge  of  the  structure. 
Numerous  experiments  of  this  kind  were  made,  and  for  many  important 
facts  we  have  to  thank  those  experimenters  who  proceeded  in  this  way.  For 
example,  through  the  nerve-cutting  experiments  of  Singer  and  of  Schieffer- 
decker  and  later  of  Lowenthal,  Sherrington,  Mott,  et  al,  our  knowledge  of 
the  course  of  nerve-roots  in  the  spinal  cord  has  been  much  enriched. 

Such  degenerations  may  be  studied  according  to  one  or  the  other  of 
two  methods:  One  may  either  wait  for  the  complete  destruction  of  the  fibers 
and  then,  follow  the  course  of  the  atrophied  tract,  or  one  may,  within  a 
few  weeks  after  the  operation,  treat  a  preparation  with  a  solution  of  osmic 
acid,  which  blackens  the  products  of  degeneration  (Marchi).  The  last 
method  especially  gives  very  clear  pictures,  showing  the  degenerated  fibers 
in  lines  of  black  points  upon  a  clear  field. 

If,  in  a  newborn  animal,  peripheral  or  central  nerve-substance  be  re- 
moved, fibers  involved  in  the  injury  or  operation  do  not  further  develop, 
but,  in  fact,  gradually,  yet  completely,  degenerate. 

Gudden  (1870)  used  this  fact  to  furnish  us  with  a  new  and  fruitful 
method  of  investigation.  For  example,  after  extirpation  of  an  eye  he  fol- 
lowed, through  means  of  sections,  the  atrophy  taking  place  in  the  brain, 
and  so  found^  the  central  ending  of  the  optic  nerve  in  question.  On  what- 


8 


ANATOMY    OF    THE    CENTRAL    NERVOUS    SYSTEM. 


ever  part  of  the  brain  he  experimented  he  brought  new  and  important  things 
to  light.  In  addition  to  Gudden  we  are  also  indebted  to  Mayser,  Ganser, 
Forel,  Monakow,  and  Lowenthal  for  important  facts  regarding  the  course  of 
fibers  in  the  spinal  cord,  the  method  of  origin  of  cranial  nerves,  the  course 
of  the  Tractus  tecto-bulbaris  in  the  brain,  etc. 

Occasionally  cases  are  observed  when  nature  herself  similarly  performs 
a  Gudden  experiment  upon  man.     The  author  was  able,  in  one  case,  to 


Ce]4 


Rdf 


Baf 


Fcp 


Cea 


/ 

B  {'ho  Fli 

Fig.  1. — Showing  the  fibres  of  the  corpus  callosum  prepared  by  teasing  with 
forceps  the  hardened  tissue.     (After  Henle.) 

follow  far  up  the  spinal  cord  atrophied  nerve-tracts  which  had  been  arrested 
in  development  through  intra-uterine  amputation  of  an  arm;  at  another 
time  opportunity  was  offered  to  study  the  nervous  system  of  a  child  which, 
soon  after  birth,  suffered  an  extended  softening  of  the  cortex  of  the 
parietal  lobes.  In  the  spinal  cord  the  crossed  pyramidal  tracts  were  com- 
pletely lacking. 

The  knowledge  of  the  course  of  nerve-tracts  has  made  notable  progress 


HISTORY   AND    METHODS    OF    INVESTIGATION.  V 

through  the  methods  of  secondary  degeneration  and  of  atrophy.  But  a  still 
more  fruitful  source  of  knowledge  is  a  new  method  based  upon  the  study 
of  the  development  of  the  nerve-sheath. 

To  Flechsig  is  due  the  merit  of  introducing  and  of  exhaustively  util- 
izing this  new  method.  In  a  series  of  communications  (1872-1881),  and 
later  «i  a  larger  work  on  the  "  Conducting  Paths  in  the  Brain  and  Spinal 
Cord"  ("Leitungsbahnen  im  Gehirn  u.  Eiickenmark,"  1876),  he  showed 
that  the  different  nerve-tracts,  which,  in  sections  of  the  central  nervous 
system  of  an  adult,  appear  so  similar  and  uniform,  differ  essentially  in  the 
embryonic  period  and  that  they  acquire  their  medullary  sheath  at  different 


Fig.  2. — For  description,  see  text. 


times.  Whole  "systems"  in  the  cross-section  of  the  spinal  cord  are  still 
transparent  at  a  time  when  others  have  already  become  white  and  medul- 
lated.  The  tracing  of  the  white  portions  in  cross-sections  and  longitudinal 
sections  is  much  easier,  and  gives  much  more  reliable  results  than  does  the 
tracing  of  fasciculi  in  fully-developed  organs. 

A  good  idea  of  the  peculiarities  of  the  results  of  the  methods  thus  far 
mentioned  may  be  had  from  a  study  of  the  accompanying  figures.  Fig.  1 
shows  the  result  of  a  dissection,  a  separation  of  the  fibers  with  forceps,  and 
shows  the  course  in  the  cerebrum  of  the  fibers  of  the  corpus  callosum. 

Fig.  2  is  made  from  a  frontal  section  through  the  cerebrum  of  a  nine- 


10  ANATOMY    OF   THE    CENTBAL   NEKVOUS    SYSTEM. 

months'  still-born  foetus.  The  whole  of  this  area  is,  in  the  adult,  filled  with 
nerve-fibers,  which  are  difficult  to  follow  because  of  their  various  directions 
and  intersections.  In  the  section  in  question,  however,  of  all  the  numerous 
fibers  of  the  cerebrum  only  the  single  tract  designated  the  tegmental  tract 
is  medullated.  In  the  figure  the  black  lines  locate  it.  At  no  other  place  in 
the  cerebrum  may  medullated  fibers  be  found.  Hence  Flechsig  was  able  to 
discover,  among  the  numerous  little-known  tracts  of  the  cerebrum,  the 
tegmental  tract  as  a  distinct  one,  and  in  part  to  trace  its  course. 

Fig.  3  represents  a  section  through  the  cervical  portion  of  a  spinal 
cord  from  a  man  who  lost  the  left  forearm  before  birth.  Note  that  both 
gray  and  white  substances — but  particularly  the  former — are  strongly  atro- 
phied on  the  left  side.  The  exact  determination  of  the  extent  of  the 
atrophy  justifies  a  conclusion  as  to  the  location  of  the  central  ends  of  the 
divided  nerves. 


Fig.  3. — For  description,  see  text. 


Knowledge  of  the  general  morphology  of  the  central  nervous  system 
is  gained  through  embryology.  For  our  knowledge  of  the  embryology  of 
the  organs  we  are  now  studying  we  are  indebted  especially  to  Kolliker,  His, 
Tiedemann,  Eeichert,  v.  Mihalkovics,  Gotte,  and  Kupffer. 

As  early  as  the  seventeenth  century  the  first  attempts  were  made  to 
approach  the  brain  in  a  comparative  way;  and  the  literature  of  the  first 
half  of  this  century  contains  a  great  number  of  monographs  on  the  brain 
of  the  lower  vertebrates.  It  was  the  fish-brain  that  was  ever  the  subject 
of  renewed  study.  The  numerous  studies  of  this  time  reached  a  climax  in 
the  work  of  Leuret  and  Gratiolet,  on  "The  Vertebrate  Brain";  also  in 
such  really  great  monographs  as  that  of  the  Wolmar  physician,  Dr.  Girgen- 
sohn,  on  "The  Brain  of  Fishes"  (1846).  Naturally  all  of  these  works  are 
concerned  simply  with  the  outer  form  of  the  brain.  That  is  true,  also,  of 
several  later  ones,  which,  undertaken  from  the  stand-point  of  general 
morphology,  have  given  us  exact  knowledge  regarding  simply  the  external 


HISTOKY    AND   METHODS    OF    INVESTIGATION.  11 

form.  Among  these  may  be  mentioned  the  works  of  Gottsche,  Viault,  Val- 
entin, Miclucho-Maklay,  Baudelot,  et  al,  who  have  given  with  exactness  the 
anatomy  of  the  selachian  and  teleostean  brain.  The  brain  of  the  am- 
phibian and  of  the  reptile  has  been  much  studied  by  comparative  anatomists; 
there  is,  however,  little  of  the  older  literature  useful  to  the  general  mor- 
phologist  except  the  works  of  Treviranus  and  of  Carus. 

But  here  was  introduced  the  new  technique  of  serial  sections.  Eeissner 
and,  later,  Stie'da  were  first  to  attempt  to  find  their  way  through  the  difficult 
field  by  the  aid  of  sections,  and  to  the  last-named  author  we  are  especially 
indebted  for  pioneer  studies  on  the  inner  structure  of  the  brain  of  the  lower 
vertebrates.  After  Stieda  had  sectioned  and  figured  the  brains  of  repre- 
sentative fishes,  amphibians,  and  birds,  there  rapidly  followed  other  studies 
in  the  same  field.  Nearly  all  classes  of  animals  were  investigated.  Fritsch 
devoted  a  beautiful  monograph  to  the  study  of  fishes.  His  statements,  how- 
ever, were  later  extended  and  in  part  much  modified  through  a  work  by  May- 
ser:  a  work  which  should  be  counted  among  the  classics  of  brain-literature. 
Along  with  Mayser's  monograph  stands  a  work  which  may  be  especially 
recommended:  "The  Description  of  the  Brain  of  Petromyzon,"  by  Ahlborn. 
These  works  have  laid  the  foundation  for  our  present  knowledge  of  the 
brain  of  the  lowest  vertebrates.  Still,  for  want  of  good  technique,  they  have 
been  able  to  give  but  little  relative  to  the  minute  structure. 

The  investigations  of  the  Italian,  Giuseppo  Bellonci,  alone  showed 
what  problems  still  resisted  solution.  Although  Bellonci  died  young,  the 
few  short  papers  which  he  left  belong  to  the  very  best  that  we  possess  in 
this  field.  Our  knowledge  of  the  brain  of  the  lower  vertebrates  was  given 
an  especial  impetus  through  the  embryological  and  comparative  anatomical 
studies  of  Etickhardt,  to  whom,  next  to  Stieda,  we  owe  the  possibility  of 
tracing  the  homology  of  single  brain-structures  of  the  lower  vertebrates  with 
the  corresponding  parts  of  the  much  better  known  mammalian  brain.  In 
America,  where  Mason  had  already  published  a  comparative  anatomical 
chart,  we  may  mention  Spitzka  and  his  pupils;  then  Osborn,  to  whom  we 
are  indebted  for  important  studies  in  commissures  and  on  the  amphibian 
brain;  and  Herrick,  who  with  great  industry  studied  representatives  of 
every  lower  class.  In  England  appeared  the  studies  of  Saunders.  In  Ger- 
many Wiedersheim,  Koppen,  Meyer,  the  author,  and  others  were  actively 
at  work.  From  Australia  we  have  received  from  Elliot  Smith  excellent 
studies  on  the  brain  of  lower  mammals.  But  for  the  most  part  the  methods 
were  yet  quite  insufficient;  so  that,  despite  much  work,  little  reliable  ma- 
terial was  collected.  The  Amphibia  and  Eeptilia  have  been,  comparatively 
speaking,  best  worked,  although  certain  parts  of  the  fish-brain  are  at  least 
fairly  well  known.  The  knowledge  of  the  avian  brain  is  most  fragmentary. 
Its  cerebral  hemispheres  have  been  studied  quite  insufficiently,  though, 


12  ANATOMY   OF   THE    CENTRAL   NERVOUS    SYSTEM. 

through  the  studies  of  S.  E.  y  Cajal,  Van  Gehuchten,  and  Brandis,  some- 
thing at  least  is  known  of  the  mesencephalon  and  of  the  origin  of  nerve- 
tracts.  The  most  important  study  of  the  avian  brain  is  that  of  Bumm. 

The  establishing  of  homologies  has  been  more  and  more  facilitated 
through  Buikhardt's  studies  in  comparative  anatomy  and  through  the  em- 
bryological  work  of  Kupffer  and  of  His.  Through  these  studies  we  first 
learned  to  recognize  the  importance  in  comparative  studies  of  invaginations 
and  evaginations  observable  upon  the  brain. 

Comparative  anatomy  has  not,  up  to  the  present  time,  increased  our 
knowledge  of  the  course  of  nerve-tracts  as  much  as  we  were  justified  in 
expecting.  The  interest  in  the  minute  structure  has  been  slight  compared 
with  that  in  the  determination  and  description  of  the  outer  form,  notwith- 
standing the  fact  that  the  former  is  the  kernel,  while  the  latter  is  but  the 
outer  shell.  This  may  be  attributed  to  the  inadequacy  of  the  methods 
which  were  at  command.  Only  a  few  were  able  clearly  to  recognize,  in  the 
labyrinth  of  tracts, — present  even  in  the  lowest  invertebrates, — single  fas- 
ciculi, or  to  differentiate  single  ganglia  and  nerve-origins.  Simple  and  clear 
as  are  the  outer  features  of  the  lower  vertebrate  brain,  the  inner  structure 
is,  nevertheless,  hardly  less  complicated,  especially  in  those  regions  posterior 
to  the  Thalamencephalon,  than  in  the  mammals  themselves.  The  cells  and 
nerve-tracts  which  are  involved  in  the  simplest  motor,  sensory,  or  psychical 
apparatus  must,  indeed,  be  everywhere  the  same,  and  they  are  not  alto- 
gether simple  and  clear  even  in  so  low  a  form  as  the  larva  of  the  cyclostomii. 

That  the  solution  of  the  problem  might  be  more  nearly  reached,  the 
author  has  endeavored  to  combine  the  comparative  anatomical  methods  with 
the  study  of  nerve-sheath  development. 

We  are  now  able  to  stain  and  to  trace  every  individual  nerve-sheath.  In 
fact,  the  comparative  embryological  method  succeeded  finally  in  finding  in 
the  embryos  of  the  lower  vertebrates  the  very  simple  relations  sought  for 
and  to  fix  definitely  upon  a  number  of  nerve-tracts  as  common  to  all  verte- 
brates. 

Of  the  very  greatest  importance  for  our  general  idea  of  the  nervous 
system  were  the  discoveries  which  followed  upon  the  Golgi  impregnation 
method  and  upon  the  Ehrlich  method  of  vital  staining  with  methyl-blue. 

Through  this  amplification  of  the  method  we  are  finally  in  a  position 
to  reach  a  clearer  understanding  of  the  relations  of  the  cells  to  each  other 
and  to  obtain  a  more  definite  idea  of  the  minute  structure  in  general. 

To  these  methods  we  are  indebted  for  the  most  important  discoveries 
made  in  recent  years,  for  the  insight  into  the  previously-unknown  nervous 
system  of  the  invertebrates,  and  for  Eetzius'  happy  discovery:  that  the  en- 
tire nervous  system  of  an  invertebrate  may,  under  certain  circumstances,  be 
seen  in  its  complete  connections.  Through  the  excellent  work  of  this  in- 


HISTOKY   AND    METHODS    OF   INVESTIGATION.  13 

vestigator  we  have  become  familiar  with  the  peripheral  and  central  nervous 
systems  of  representatives  of  numerous  classes  of  invertebrates.  The  vital 
methyl-blue  staining,  which  more  than  any  other  has  made  these  results 
possible,  is  very  perishable,  and  work  with  it  is  difficult,  requiring  exact 
estimation  of  the  proper  time,  etc.  So  the  process  recently  taught  by  Bethe 
for  fixing,  hardening,  and  cutting  the  tissue  stained  with  methyl-blue  was 
welcomed  gladly. 

It  is  to  be  expected  that  the  method  in  its  present  perfection  will  make 
possible  an  especially  rapid  progress  of  knowledge. 

The  means  to  the  end  are  many.  For  every  single  problem  one  must 
always  ask  the  question:  What  method  is  to  be  applied  that  one  will  have 
to  meet  only  the  simplest  relations?  Seldom  will  the  study  of  the  organs 
of  adult  man  lead  to  trustworthy  results;  it  will  usually  be  necessary  to 
create  artificially  greater  simplicity. 

From  time  to  time  it  has  been  attempted  to  comprise  in  a  schematic 
drawing  what  was  known  of  the  minute  anatomy  of  the  nervous  system. 
The  oldest  schematic  representation  of  the  brain-tracts  known  to  the  author 
is  that  of  Descartes,  in  "Tractatus  de  Homine,"  which  appeared  in  1662. 
Among  the  older  representations  belonging  to  this  class  may  be  enumerated: 
schemes  of  the  spinal  cord  by  Kolliker,  by  Ludwig,  by  Bidder,  and  by 
Leydig,  and  the  renowned  schema  of  Stilling.  The  diagrams  of  Meynert, 
of  Aeby,  and  of  Flechsig  include  a  larger  field, — from  the  spinal  cord  to  the 
Corpora  Quadrigemina, — while  that  of  Jelgersma  includes  the  entire  nerv- 
ous system. 

In  the  following  chapters  the  reader  will  often  find  in  the  figures  and 
in  the  statements  what  is  really  only  a  sort  of  schema.  Such  a  method  serves 
the  purpose  of  presenting  in  the  clearest  possible  way  the  most  important^ 
facts  regarding  the  nerve-tracts  of  the  central  nervous  system.  Not  only 
are  lines  drawn  to  represent  facts  won  by  purely  anatomical  methods,  but 
also  to  represent  those  tracts  which  could  be  determined  by  well-observed 
pathological  facts.  A  schema  is  not  always  a  picture  of  nerve-tracts;  it  is 
often  simply  a  graphic  representation  of*the  conclusions  which  may  be 
drawn  from  numerous  observations.  A  schema  is  a  tottering  structure.  It 
must  be  repaired,  sometimes  here,  sometimes  there:  or  often  in  part  torn 
down  and  reconstructed.  It  has  been  contended  that  one  has  no  right  to 
construct  schemata  in  a  field  where  there  are  so  many  deficiencies  as  in  our 
knowledge  of  the  central  nervous  system.  But  let  us  join  with  the  venerable 
Burdach,  who  wrote  in  1819:  "It  is  not  alone  necessary  to  collect  building 
material.  In  every  period  in  which  a  new  mass  of  material  is  collected  we 
must  start  anew  to  erect  an  edifice.  This  giving  of  definite  fo*rm  to  the 
knowledge  will  in  no  way  retard  the  spirit  of  inquiry  which  leads  to  new 
discoveries;  on  the  contrary,  it  is  only  when  we  get  a  comprehensive  view 


14  ANATOMY    OF    THE    CENTRAL    NERVOUS    SYSTEM. 

and  behold  the  imperfections  of  our  knowledge  that  we  know  what  direction 
future  investigations  must  take.  May  the  attempt  at  such  structures  ever 
be  renewed,  for  no  such  attempt  fails  to  advance  knowledge!" 

LITERATURE. 

Among  the  older  works  on  the  central  nervous  system  the  following  may  be 
mentioned: — 

Kolliker,  "Handbuch  d.  mikroskop.  Anat."     Leipzig,  1854. 

Meynert,  "Vom  Gehirne  der  Saugethiere" :  "Strieker's  Handb.  d.  Lehre  von  den 
Geweben."  1870. 

Meynert,  "Psychiatric."     I.     Wien,  1884. 

Henle,  "Handbuch  d.  Anatomic  d.  Nervensystems."     Braunschweig,  1879. 

Luys,  "Recherches  sur  le  Systeme  nerveux  cerebrospinal."     Paris,  1865. 

W.  Krause,  "Handb.  d.  menschl.  Anatomic."    I.  Bd.    Hannover,  1876. 

Wernicke,  "Lehrb.  d.  Gehirnkrankh."    I.    Cassel,  1881. 

Schwalbe,  "Lehrb.  d.  Neurologic."  Erlangen,  1881.  (Contains  most  of  the  litera- 
ture up  to  1881.) 

Huguenin,  "Allg.  Pathol.  d.  Krankh.  d.  Nervensystems."    I.     Zurich,  1873. 

Kahler,  "Nervensystem  in  Told's  Gewebslehre."     2  Aufl.     1888. 

Newer  works: —  « 

7.  Lenhossek,  "Der  feinere  Bau  des  Nervensystems."    2  Aufl.    Berlin,  1895. 

8.  Ram6n  y  Cajal,  "Neue  Darstellung  vom  histol.  Bau  des  Nervensystemes.'r 
Arch.  f.  Anat.  u.  Phys.  Anat.  Abth.  1893.    Translated  into  several  languages. 

V.  Horsley,  "The  Structure  and  Functions  of  the  Brain  and  Spinal  Cord."  Lon- 
don, 1892. 

Obersteiner,  "Anleitung  beim  Studium  des  Baues  der  nervosen  Centralorgane." 
3  Aufl.  Wien,  1896. 

Mendel,  Artikel  "Gehirn"  in  Eulenburg's  Realencyklopadie.    3  Aufl.    Wien,  1895. 

Fere,  "Traite"  elementaire  d'Anatomie  medicale  du  systeme  nerveux."  2.  Aufl. 
Paris,  1891. 

Brissaud,  "Anatomic  du  cerveau  de  1'homme."    Atlas  and  Text.    Paris,  1893. 

Van  Gehuchten,  "Le  systSme  nerveux  de  1'homme."    Lierre,  1893. 

Charpy,  "SysteTne  nerveux,"  in  Poirier's  "Traite  d'Anatomie  humaine."  Paris, 
1894. 

Kolliker,  "Handbuch  d.  Gewebelehre."    Bd.    II. 

Bechterew,  "Die  Leitungsbahnen  u.  s.  w."    Leipzig,  1894. 

J.  Dejerine  and  Madame  D6j$rine-Klumpke,  "Anatomic  des  centres  nerveux." 
Paris,  1895. 

Quite  complete  reviews  of  all  monographs  in  the  field  of  brain-anatomy  have 
appeared  since  1885  in  "Schmidt's  Jahrbiichern  der  gesammten  Medicin." 

The  active  work  in  this  field  is  shown  by  the  fact  that  between  1885-1894  not 
fewer  than  1285  studies  in  the  anatomy  of  the  central  nervous  system  were  reviewed 
in  this  periodical. 


CHAPTER    II. 
FUNDAMENTAL  CONCEPTIONS  :    GANGLION-CELL  AND  NERVE. 

THE  significance  and  position  of  the  central  nervous  system  of  the 
Vertebrates  can  only  be  understood  when  one  takes  into  consideration  its 
development,  its  relation  to  the  peripheral  nerve-endings,  and  to  the  organs 
of  special  sense. 

The  central  apparatus  stands  in  no  wise  so  isolated  or  so  separated, 
through  morphological  or  physiological  differences,  from  the  peripheral 
apparatus  as  it  was,  until  recently,  supposed  to  be. 

Among  both  vertebrates  and  invertebrates  both  systems  are  derived 
from  the  outer  embryonic  layer:  from  the  epiblast.  In  vertebrates  a  part  of 
this  thin  lamella  forms  a  deep,  longitudinal  groove  which,  gradually  closing 
in  and  separating  from  the  remainder  of  the  epiblast,  becomes  the  tubular 
fundament  of  the  central  nervous  system.  Another  part  of  the  epiblast, 
lying  close  beside  the  groove  on  either  side,  forms  the  fundament  of  the 
spinal  and  cranial  ganglia.  Many  widely-disseminated  places  produce  cells 
which,  even  in  the  higher  animals,  either  remain  in  the  periphery  and  form 
cutaneous  sense-organs  or  they  sink  more  or  less  deeply  and  form  the 
fundament  of  other  sense-organs;  for  example,  the  olfactory  or  auditory 
apparatus  or  the  apparatus  of  equilibration.  This  relatively  simple  picture 
becomes  somewhat  more  complicated  in  that  many  fundaments,  which 
among  invertebrates  remain  completely  peripheral,  among  the  vertebrates 
lie  close  beside  the  central  system,  fusing  with  it.  It  is  further  complicated 
in  that,  when  the  neural  groove  is  once  closed,  cell-groups  wander  out  from 
it  into  the  periphery,  there  later  to  become  independent  and  scattered 
ganglia. 

The  longitudinal,  laminated,  epithelial  plate  which  curved  in  to  form 
the  groove  representing  the  fundament  of  the  central  nervous  system  is 
called  the  medullary  plate.  Very  early  there  appear  in  it,  in  all  classes  of 
vertebrates,  changes  which  lead  to  the  formation  of  different  kinds  of  cells. 
Among  the  epithelial  cells,  and  formed  from  them,  appear  the  Germ-cells'. 
large,  round,  protoplasmic  structures, — the  fundaments  of  the  future 
ganglion-cells.  The  axis-cylinders  grow  from  them  later,  and  still  later 
numerous  otfier  processes  arise  from  the  cell-body,  thus  stamping  the  cell 
as  a  multipolar  one. 

Epithelial  cells  remain,  in  part,  as  the  boundary  of  the  central  canal  of 

(15) 


16 


ANATOMY   OF    THE    CENTEAL   NEEVOUS    SYSTEM. 


the  nervous  system.  Then  in  all  vertebrates  they  send  peripherally  a  process 
which  persists  until  in  adult  life  and  which  is  usually  somewhat  branched 
and  ends  close  beneath  the  pia.  There  one  often  meets  curious  enlargements 
of  the  cell-extremity,  from  which,  as  in  the  epithelial  cells  of  the  sense- 
organs,  a  delicate  bristle-like  projection  rises.  In  man  and  the  higher 
mammals  the  epithelial  processes  do  not  appear  to  reach  the  periphery  in 
the  post-embryonic  period.  The  epithelium  of  the  central  canal  is  ciliated. 


Fig.  4. — A,  B,  Ganglion-cells;    c,  Neuroglia-cells;    Z),  Axis-cylinder;    p,  Proto- 
plasmic processes.     From  the  spinal  cord.      (After  Ranvier.) 


But  not  by  any  means  are  all  epithelial  cells  employed  in  lining  the 
central  canal.  Through  cell-division  there  arise  very  many  new  structures, 
and  one  finds  that  these  recede  farther  and  farther  from  the  central  canal, 
with  whose  wall  they  often  remain  in  connection  through  a  fine  fibre.  The 
branching  processes  of  these  cells  form  a  net-work  which,  in  the  adult,  may 
permeate  the  whole  substance  of  the  central  nervous  system,  being  more 
dense  in  some  locations  than  in  others.  His,  their  discoverer,  called  these 


GANGLION-CELL   AND    NERVE.  17 

cells,  which  form  a  part  of  the  frame-work,  the  Spongioblast ;  he  designated 
the  incomplete  ganglion-cells  Neuroblasts. 

When  the  central  nervous  system  has  once  passed  its  first  stage  of  de- 
velopment practically  the  same  histological  relations  manifest  themselves 
as  one  meets  in  the  adult  condition.  Let  us  turn  our  attention  briefly  to 
these. 

The  whole  central  nervous  system  is  constructed  of  connective  tissue 
and  nerve-tissue.  The  first  is  represented  by  the  sheathes  of  the  numerous 
vessels,  which  permeate  the  organs  everywhere  as  a  dense  net-work,  and  by 
the  neuroglia. 

The  neuroglia  consists  of  an  infinite  number  of  fine  fibrillas,  of  very 
different  caliber,  which  permeate  the  whole  central  system,  and,  because  of 
the  innumerable  intersections,  present  the  appearance  of  a  fine  mesh-work. 
At  many  of  these  points  of  intersection  thin  plate-cells  lie  upon  the  fibers, 
giving  rise  to  the  appearance  of  neuroglia-fibers  (Gliafasern)  arising  from 
these  cells, — Deiter's  cells  (see  Fig.  4,  c). 

The  neuroglia-net  differs  somewhat  in  different  parts  of  the  central 
nervous  system,  and  forms  here  and  there  dense  accumulations  in  parts  quite 
devoid  of  nerve-substance.  Thus,  a  thick  layer  of  nearly  pure  connective 
tissue  covers  the  whole  surface  of  the  brain  and  cord  and  extends  a  short 
distance  along  the  nerve-roots  in  the  form  of  a  plug.  In  the  same  way 
there  is  found  on  the  inner  surface  of  the  central  nervous  system  just  under 
the  epithelium  an  especially  rich  development  of  neuroglia.  The  net-work 
in  the  gray  substance  is  in  some  parts  denser,  in  others  less  dense,  than  in 
the  white  substance.  The  larger  nerve-cells  are  frequently  so  encircled  that 
they  appear  to  lie  in  a  fine  meshed  basket. 

The  neuroglia  is  a  peculiar  tissue  found,  as  yet,  only  in  the  central 
nervous  system, — except  that  the  optic  nerve  possesses  glia.  It  may  be 
absolutely  differentiated  from  other  kinds  of  tissue  by  its  peculiar  reaction 
to  staining  when  in  pathological  conditions.  Wherever  in  the  central  nerv- 
ous system  nerve-substance  degenerates  through  disease,  the  glia  (neuroglia) 
appropriates  the  empty  space.  The  replacement  with  glia  has  a  limit  only 
where  its  elements  are  destroyed  along  with  the  nerve-substance  and  where 
its  power  of  growth  is  not  sufficient  to  fill  up  the  large  deficit. 

It  has  already  been  mentioned  that  the  epithelium  of  the  central  canal 
and  the  ventricles  sends  long  processes  into  the  surrounding  nerve-substance. 
In  man  these  reach  the  external  surface  only  in  a  few  places.  These  fibers, 
an  instructive  figure  of  which  is  here  presented  (Fig.  5),  belong  naturally  to 
the  supporting,  tissues. 

In  Fig.  6  is  represented  (E]  a  section  through  the  neuroglia-net  of  the 
gray  substance  of  an  adult  man  as  it  appears  after  treatment  with  the 
Weigert  method. 


18 


ANATOMY    OF    THE    CENTRAL    NERVOUS    SYSTEM. 


The  real  nerve-tissue  which  fills  the  meshes  of  the  figured  net-work 
consists  of  ganglion-cells  and  nerve-fibers.  The  form  of  the  ganglion-cells 
is  exceedingly  varying.  There  are  small,  nearly-spherical  forms  with  few 
processes,  and  there  are  multipolar  cells  with  numerous  processes  and  twenty 
times  as  large  as  the  ones  just  described.  In  the  lobes  of  the  N".  vagi  of  the 
Torpedo  and  in  the  Medulla  of  the  Cyclostomii  are  ganglion-cells  so  enor- 


Fig.  5. — Epithelium  and  neuroglia  surrounding  the  central  canal.  Section, 
through  the  spinal  cord  of  a  human  embryo  of  twenty-three  centimeters'  length. 
Prepared  by  the  Golgi-Cajal  method.  Note  that  only  a  part  of  the  cells  have 
taken  the  silver  precipitate, — a  marked  advantage  mentioned  above, — for  only 
through  this  is  it  possible  to  recognize  what  belongs  to  any  one  cell.  (After 
Lenhossek.) 


mous  that  one  may  easily  see  them  with  the  unaided  eye.  Indeed,  in  the 
spinal  cord  of  the  electric  eel — Malapterurus — are  two  isolated  ganglion- 
cells  of  such  size  that  the  immense  single  nerve-fiber  which  each  sends  out 


•• 


Fig.  6.— ^4.  and  B,  Cells  from  the  anterior  horn  of  a  human  spinal  cord. 
Fixed  with  alcohol  and  stained  with  methyl-blue.  C,  Ganglion-cell  fixed  with 
alcohol  and  stained  with  haematoxylin.  D,  Ganglion-cell  from  anterior  horn  of 
fetal  dog.  (After  an  original  preparation  by  Ramon  y  Cajal.)  Prepared  with 
Golgi  method.  E,  Neuroglia.  (After  an  original  preparation  by  Weigert.)  Neu- 
roglia-fibers  blue;  axis-cylinders  black.  (After  an  original  preparation  by  Nissl.) 


20  ANATOMY    OF   THE    CENTEAL   NERVOUS    SYSTEM. 

suffices  to  innervate  the  large  electric  organ.  Quite  different  appearances  are 
obtained  according  to  the  technique  used  in  the  preparation  of  the  ganglion- 
cells.  In  Fig.  4  two  ganglion-cells  are  represented  as  they  appear  after 
treatment  with  carmin  and  picrocarmin.  Fig.  6  (D)  shows  a  cell  treated 
according  to  the  Golgi  method  in  which  the  silver  precipitate  shows  the 
processes  in  a  beautiful  way  before  unequaled.  Of  the  structure  of  the  cell 
nothing  can  be  seen.  Structural  figures,  important  in  investigations  in  the 
realm  of  pathology,  are  only  gotten  in  other  ways.  Fig.  6  (A  and  B)  shows 
what  microscopic  technique  has  accomplished  up  to  the  present  time. 
Many  ganglion-cells  bear  pigment  of  yellowish-brown  color.  In  the  two 
cells  figured  the  pigment  is  indicated  in  dotted  black. 

The  nerve-fibers  originate  from  the  ganglion-cells.  "Wagner  first 
showed  that  in  many  of  these  cells  only  one  process  may  be  followed  directly 
into  a  nerve,  and  other  investigators  have  confirmed  it.  This  process  is 
called  a  Neuraxon,  an  Axis-cylinder  Process,  or  a  Neurite.  What  became  of 
those  neuraxons  which  did  not  pass  into  nerve-trunks;  what  role  was  played 
by  the  other  processes  of  the  cell, — the  protoplasmic  processes,  or  Den- 
Writes,— remained  in  complete  obscurity  until  Gerlach  stated  in  1870  that 
all  these  form  among  themselves  a  net,  and  from  this  there  arise  nerve- 
fibers  again. 

In  the  course  of  the  last  few  years  our  knowledge  has  undergone  an 
unexpectedly  extensive  amplification,  made  possible  by  the  progress  of  his- 
tological  and  of  histo-physiological  technique.  First  Bellonci,  through 
osmium  staining,  then  still  more  conclusively  Golgi,  through  treatment  of 
the  cells  with  sublimate  or  even  with  silver  precipitates,  succeeded  in  demon- 
strating that  from  some  cells  the  neuraxon  passes  directly  into  a  nerve-fiber, 
but  from  other  cells  neuraxons  arise  which  break  up  into  a  net-work. 
Lateral  twigs  coming  from  those  neuraxons  which  arise  from  the  first- 
described  cells  are  said  to  take  part  also  in  the  formation  of  this  net-work. 
Golgi  supposed  that  nerve-fibers  pass  out  again  from  the  net-work.  There 
is  then  a  twofold  origin  for  nerve-fibers:  one  direct,  the  other  indirect, 
through  the  means  of  the  net-work.  The  dendritic  processes,  it  is  asserted, 
have  nothing  to  do  with  the  formation  of  nerve-fibers.  Such  were  the 
results  of  Golgi's  observations. 

What  Golgi  inferred  from  the  study  of  numerous,  sometimes  compli- 
cated, views  of  the  brain-cortex  and  spinal  cord  of  man  and  mammals, 
Haller  was  able  to  see  directly  in  the  ganglia  of  mollusks  and  worms,  where 
the  histological  relations  are  very  distinct.  But,  according  to  his  view,  the 
net-work*  arises  from  cell-processes  which  are  essentially  equivalent  one  to 
another.  Through  these  studies,  as  well  as  those  of  Nansen  and  others, 
the  proof  seemed  conclusive  that  there  are  two  modes  of  origin  of  nerve- 
fibers:  a  direct  one  and  one  through  the  medium  of  a  net- work. 


GANGLION-CELL   AND    NERVE.  21 

But  it  soon  became  apparent  that  this  valuable  discovery  had  only 
opened  the  way  to  other  much  more  significant  ones:  that  it  held  only  a 
part  of  the  truth.  A  Spanish  scholar,  Kamon  y  Cajal,  who  worked  with  the 
Golgi  silver  method,  published  in  close  succession  a  series  of  studies  whose 
results — confirmed  and  amplified  by  Kb'lliker,  Gehuchten,  Waldeyer,  Len- 
hossek,  and  others — lead  us  to  new  views.  We  stand  yet  in  the  current  of 
changing  opinions,  receiving  daily  new  contributions  to  this  interesting 
question.  We  can  already  picture  to  ourselves  the  minuter  relations  of  the 
elements  in  the  central  nervous  system.  But  this  picture  which  is  to  be 
developed  is  not  founded  upon  purely  anatomical  investigation.  At  the 
same  time  that  histological  preparations  brought  us  to  the  new  views,  His, 
on  the  basis  furnished  by  embryology;  Forel  and  Monakow,  from  studies 
in  the  realm  of  pathology,  came  to  a  conception  of  the  origin  and  end  of 
nerve-tracts  which  nearly  coincides  with  that  reached  by  the  anatomical 
method.  Eetzius  finally  succeeded,  indeed,  in  demonstrating,  through  vital 
methyl-blue  reactions  on  the  living  nerve-cells  of  many  lower  orders  of 
animals,  much  which  harmonizes  well  with  conclusions  from  histological 
preparations. 

The  ganglion-cells  usually  send  out  two  kinds  of  processes  from  their 
bodies:  a  moderately-fine  process,  the  neuraxon,  neurite,  or  axis-cylinder, 
which  is  first  to  spring  from  the  cell;  and  the  thicker  dendrites  or  proto- 
plasmic processes,  which  break  up  into  fine  twigs.  The  dendrites  appear 
somewhat  late  in  embryonic  development.  The  neuraxons  always  end  ap- 
parently by  breaking  up  into  branches.  Two  kinds  of  cells  can  be  differ- 
entiated: (1)  those  in  which  the  process  is  so  short  that  the  ramifications 
lie  close  by  the  cell  (Fig.  152,  g]  and  (2)  those  with  long-extended  neuraxons 
(Fig.  152,  d  and  /).  Along  its  course,  which  sometimes  extends  for  many 
centimeters,  such  a  process  gives  off  more  or  less  numerous  lateral  branches, 
or  collaterals.  These  also  end,  like  the  main  process,  in  fine  subdivisions. 
We  have  long  known  that  the  neuraxon  of  a  nerve-fiber  is  composed  of 
numerous  separate  fibrillae.  So  there  is  nothing  striking  in  the  statement 
that  along  the  course  of  the  nerve  individual  fibrillaB  branch  off  from  the 
main  trunk.  Naturally,  one  has  very  infrequent  opportunity  to  follow  a 
neuraxon  with  certainty  from  its  origin  to  its  end.  But  all  that  has  been 
learned  regarding  the  termination  of  this  important  cell-process, — what  has 
been  observed,  and  what  has  been  inferred  from  prepared  specimens, — in- 
dicates that  it,  in  truth,  branches  out  into  fibrillas  at  its  termination.  If 
it  passes  out  from  the  central  system  to  the  periphery,  as  in  the  spinal  nerve- 
roots,  it  ramifies  in  the  muscle-tissue — motor  end-plates — or  between  epi- 
thelial cells — plexuses  of  the  sense-organs.  But  relatively  few  of  the  neu- 
raxons pass  to  the  peripheral  organs.  Very  much  the  greater  part  of  them, 
after  a  shorter  or  longer  course,  come  into  relation  with  another  cell,  grasp- 


22  ANATOMY    OF   THE    CENTEAL    NERVOUS    SYSTEM. 

ing  it  or  surrounding  it  with  its  terminal  ramification  (Endpinselung).  If 
the  cell-body  is  not  very  large,  it  has,  nevertheless,  abundant  points  of  con- 
tact through  its  numerous  dendrites;  but,  if  it  is  very  extended,  as  in  the 
cells  of  the  spinal  ganglia,  the  dendrites  are  less  needed. 

The  dendritic  processes  break  iip  into  a  more  or  less  abundant  branch- 
ing, whose  surface  may  be  further  increased  by  the  presence  of  innumerable, 
small,  pedunculated  knots  (Fig.  152,  Z).  A  transformation  of  dendritic 
fibers  into  peripheral  (efferent)  nerves  has  not  been  demonstrated.1 

On  the  physiological  significance  of  the  dendrites  there  are  great  differ- 
ences of  opinion.  According  to  the  author's  investigations  and  from  what 
may  be  learned  from  figures  contributed  by  others,  it  seems  most  probable 
that  the  dendrites  represent  an  increase  of  surface  of  the  ganglion-cell,  which 
is  absolutely  necessary  to  insure  intimate  relations  with  the  surrounding 
fibers  of  neuraxons  (from  other  cells).  In  Fig.  16  may  be  seen  (a)  the 
terminal  process  of  a  sensory  cell  of  the  olfactory  epithelium  passing  as  an 
olfactory  nerve,  or  fila  olfactoria,  through  the  cribriform  plate  and  breaking 
up  into  terminal  fibrillae  in  the  olfactory  lobe  of  the  brain  (see  also  Fig.  94). 
Their  terminal  ramifications  intimately  embrace  the  dense  dendritic  fibers 
from  the  ganglion-cells  there  located.  Here  one  sees  the  relation  between 
the  olfactory  tract  of  the  first  order  and  those  cells  from  which  are  developed 
the  olfactory  tract  of  the  second  order,  whose  course  lies  within  the  olfactory 
lobe.  The  connection  is  here  established  only  through  the  relation  which 
the  neuraxon  of  one  cell  bears  to  the  dendrites  of  another. 

Dendrites  and  neuraxons  do  not  always  pass  off  from  the  cell-body  at 
different  places.  Among  the  vertebrates  one  may  often  notice  that  the 
cell  sends  out  a  process,  that  appears  quite  like  a  dendritic  process,  from 
near  the  origin  of  which  a  neuraxon  branches  off.  Among  many  inverte- 
brates this  is,  indeed,  the  rule.  In  the  river  cray-fish,  for  example,  the  pear- 
shaped  ganglion-cells  send  out  usually  one  thick  branch  from  which  the 
dendrites  branch  off  laterally  and  the  neuraxon  develops  farther  on  (Fig.  8). 
Here  appears  to  be  a  condition  which  indicates  that  the  two  kinds  of  proc- 


1  The  most  recent  writings  of  American  neurologists  show  a  practical  unanimity 
in  the  use  of  the  term  dendrite  for  the  afferent  cell-processes,  and  Neuraxon,  Axone, 
or  Neurite  for  the  efferent  cell-processes.  In  a  vast  majority  of  cases  the  dendrites 
are  short,  protoplasmic  processes  structurally,  while  the  neuraxon  is  a  long  nerve- 
fiber  having  the  structure  described  usually  as  an  axis-cylinder.  Figs.  15  and  16  make 
it  evident  that  the  afferent  sensory  nerve-fibers  are  dynamically  to  be  classified  with 
the  dendrites;  moreover,  their  development  indicates  a  similar  thing.  These  afferent 
sensory  nerves  are  structurally  axis-cylinders.  In  order  to  avoid  ambiguity  and  con- 
fusion in  this  translation,  the  term  neuraxon  will  be  uniformly  used  for  the  efferent 
cell-processes.  If  the  term  axis-cylinder  is  used  it  will  be  understood  to  apply  strictly 
to  the  structure  of  the  fiber. — W.  S.  H. 


GAXGLIOX-CELL    AXD    XERVE.  23 

esses  of  a  ganglion-cell  are  not  at  all  absolutely  and  fundamentally  different 
from  each  other. 

The  developmental  unit — which  comprises  ganglion-cell,  neuraxon, 
dend rites,  and'their  ramifications — is  called  a  neuron.  It  is  probable  that  the 
entire  nervous  system  is  composed  of  numerous  neurons,  built  one  upon 
another.  The  majority  of  these  neurons  appear  to  stand  isolated,  only  con- 
nected to  neighboring  neurons  through  a  contact  so  intimate  as  easily  to 
make  possible  the  transmission  of  physiological  processes.  Purely  morpho- 
logical studies  here  lead  to  no  conclusions. 

The  labyrinth  of  fibers  found  in  almost  every  part  of  the  nervous  system 
and  the  uncertainty  of  our  present  methods  admit  too  easily  of  false  conclu- 
sions; but  the  observations  of  experimental  pathology  and  of  pathological 
anatomy  all  teach  that,  if  a  ganglion-cell  be  diseased  or  injured,  the  changes 
will  not  be  propagated  farther  than  the  processes  of  that  cell  reach.  This 
is  demonstrable  on  the  axis-cylinder  of  a  peripheral  nerve,  which  can  often 
be  studied  through  many  centimeters  of  its  course.  Its  condition  is  abso- 
lutely dependent  upon  the  condition  of  the  cell  from  which  it  springs. 

These  circumstances  also  indicate  that  each  ganglion-cell  stands 
isolated, — not  directly  joined  with  any  other.  It  must  be  mentioned,  how- 
ever, that  conscientious  observers  have  repeatedly  described  links  of  con- 
nection between  different  cells. 

These  are  fundamental  facts.  They  will  be  better  comprehended  after 
a  review  of  what  is  known  regarding  the  origin  and  course  of  a  single, 
thoroughly  studied  tract. 

Many  motor  nerves  arise  from  large  ganglion-cells  which  lie  in  the 
anterior  horn  of  the  spinal  cord.  From  each  of  these  cells  there  arises  one 
neuraxon.  It  passes  out  of  the  spinal  cord  as  a  nerve-root,  and  then  passes 
into  a  nerve-trunk,  within  which  its  course  lies  until  in  a  muscle  it  branches 
off  to  the  end-plate  (Fig.  7). 

That  part  of  the  system  which  reaches  from  the  periphery  to  its  first 
ending  in  the  central  system  is  designated  as  a  tract  of  the  first  order.  These 
tracts  of  the  first  order — in  this  case  including  anterior  horn,  motor  nerve, 
and  muscle-ending — have  been,  because  of  their  peculiar  relation  in  disease, 
for  years  classified  together  in  pathology  and  separated  from  the  tracts  of  a 
higher  order. 

The  further  transmission  of  the  nervous  impulse  takes  place  in  this 
manner  among  the  mammals:  to  tracts  of  the  first  order  connect  tracts  of 
the  second  order  or  even  of  the  third  and  fourth  in  succession.  All  consist 
of  these  parts:  ganglion-cell,  neuraxon,  and  ramification.  If  we  turn  to  the 
chosen  example  we  find  that,  around  the  numerous  dendrites  which  the 
ganglion-cell  of  the  anterior  horn  sends  out,  there  are  many  fine  fibrillae. 
These  fibrilla?  surround  them  without,  so  far  as  we  know,  coming  into 


24 


ANATOMY    OF   THE    CENTRAL    NERVOUS    SYSTEM. 


actual  contact  with  them.  These  fibrillse  are  in  part  collaterals  from  a  tract 
which  we  know  from  observations  in  pathology  passes  from  large  cells  in 
the  brain-cortex  downward  through  the  brain  and  spinal  cord.  This  tract 
— which  consists  again  of  brain-cell,  descending  nerve,  collaterals,  and 
ramifications — is  adapted  to  the  establishment  of  a  connection  between  the 
brain  and  the  end-plates  in  the  muscles;  it  is  the  central  segment  of  the 
motor  course  of  innervation,  or,  at  least,  a  part  of  it.  This  is  the  motor  tract 
of  the  second  order.  How  many  of  these  units  are  involved  in  a  complete 
motor  process  is  as  yet  unknown.  In  Fig.  152  one  observes  that  the  ramified 


Fig.  7. — Schematic  representation  of  the  relation  of  ganglion-cell  and 
nerve  in  a  motor  tract. 


neuraxons  of  other  cortical  cells  surround  the  dendrites  of  those  large  corti- 
cal cells  from  which  the  secondary  motor  tract  originates.  These  represent 
tracts  of  higher  order. 

Work  on  the  inner  structure  of  ganglion-cells,  for  the  revival  of  which 
we  are  especially  indebted  to  Nissl,  has  not  yet  led  to  conclusive  results, 
especially  because  the  significance  of  the  fine  lines  which  appear  after  treat- 
ment with  sublimate,  alcohol,  and  basic  anilin  stains  is  not  yet  clear;  also 
because  it  is  not  yet  always  certain  how  much  these  structural  features  may 
depend  upon  the  influence  of  the  reagents  themselves.  Nevertheless,  the 
work  of  Nissl,  who  especially  advised  fixation  with  alcohol,  has  led  to  very 


GANGLION-CELL   AND   NERVE.  25 

important  results  already  applicable.  In  the  body  of  all  ganglion-cells  one 
finds,  after  fixation  with  alcohol,  a  substance  which  stains  with  basic  stains 
and  a  substance  which  does  not.  The  first  appears  in  different  cells,  and 
probably  in  different  conditions  of  the  same  cell,  in  variable  structural 
forms.  'One  meets  granules,  threads,  and  spindles,  as  well  as  many  other 
regular  and  irregular  forms,  of  which  only  a  few  are,  through  position  or 
form,  well  characterized  (Kerrikappen,  Verzweigungslaegel,  u.  s.  w.).  This 
structural  arrangement  differs  so  greatly  that  i^issl  has,  within  the  ganglion- 
cell  genus,  separated  out  a  great  many  different  cell-species.  According  to 
this  author,  definite  differences  appear  also  within  the  nucleus,  which  he 
utilized  with  the  other  characters  in  differentiating  cells.  If  the  ganglion- 
cell  suffers  any  injury — be  it  the  influence  of  a  poison,  of  unwonted  activity, 
or  of  a  divided  axis-cylinder — changes  always  arise  within  the  stainable 
substance.  When  the  injury  is  intense  the  changes  may  lead  to  an  almost 
complete  disappearance  of  the  stainable  substance.  But  if  the  nucleus%re- 
mains  uninjured  the  integrity  of  the  cell-substance  may  be  restored. 

The  study  of  this  cell-change  is  of  the  very  greatest  importance.  It 
opens  to  us  finally  a  glimpse  into  the  inner  changes  which  proceed  during 
cell-activity. 

Hodge,  as  well  as  Nissl,  has  done  most  creditable  work  in  this  field. 
Hodge  studied  cells  fatigued  by  direct  stimulation  or  by  stimulation  through 
the  medium  of  the  axis-cylinder;  also  cells  in  the  condition  of  fatigue, — 
ganglion-cells  of  bees  after  the  day's  work, — comparing  them  with  rested 
cells.  He  found  that  the  stainable  granules  always  decreased;  that  the 
fatigued  cell  became  more  translucent;  further,  that  it  even  became  vacu- 
olated.  At  the  same  time  the  volume  decreased.  On  the  last  point,  how- 
ever, there  is  no  unanimity  of  statement. 

These  differences  are  conditioned  upon  the  present  state  of  the  tech- 
nique. Complete  unanimity  of  statement  exists  on  the  relation  of  the 
nucleus  to  fatigue.  This  always  decreases  in  size,  becomes  serrated,  and 
takes  a  darker  stain  than  the  rested  nucleus. 

Within  the  unstained  substance  the  latest  investigations  by  Becker, 
Flemming,  Dogiel,  et  al,  have  demonstrated  a  delicate  fibrillated  structure. 
The  appearance  is  as  if  each  of  the  larger  cells  studied  were  traversed 
in  all  directions  by  long,  delicate  threads,  which  pass  in  and  out  with  the 
cell-branches.  Further,  such  threads  do  not  always  traverse  the  entire  cell, 
but  pass  out  again  into  that  branch  located  next  to  the  one  by  which  it 
entered.  Becker  demonstrated  this  in  the  cells  of  the  anterior  horn.  Only 
the  improved  method  made  the  presence  of  these  fibrilla?  certain.  Possibly 
they  will  yield  a  foundation  for  a  better  knowledge  of  the  function  of  the 
ganglion-cell.  Max  Schultze  drew  attention  to  them,  however,  many  years 
ago. 


26  ANATOMY    OF   THE    CENTRAL    NERVOUS    SYSTEM. 

One  looks  upon  the  ganglion-cells  and  their  branches  as  elements  which 
bear  the  function  of  the  central  nervous  system.  Even  in  very  low-ranked 
animals  they  appear  isolated  or  gathered  into  knots:  ganglion-knots.  Ac- 
cording as  these  ganglia  lie  isolated  peripherally  or  collected  in  a  particular 
arrangement  and  joined  with  each  other  by  nerve-trunks  they  are  classified 
as  peripheral  ganglia  or  as  central  nervous  system.  In  general,  it  is  recog- 
nized that  in  the  animal  kingdom  there  is  a  tendency  toward  the  gathering 
of  many  ganglia  into  a  single  nervous  system.  The  higher  the  rank,  the 
larger  is  this  system;  but  until  the  vertebrate  rank  is  reached  there  are  im- 
portant parts  of  the  nervous  system  always  more  or  less  separated  and 
functionally  as  well  as  anatomically  more  or  less  independent. 

Physiology  shows  how  not  only  the  individual  ganglia  which  lie  in  the 
intestines  function  with  relative  independence,  but  how  even  structures  like 
the  spinal  ganglia,  frequently  reckoned  in  with  the  central  system,  still 
enjoy  relative  independence  from  it  functionally. 

What  we  know  of  the  anatomical  structure  and  of  the  functions  of  the 
central  nervous  system  of  vertebrates  forces  us  more  and  more  to  the  conclu- 
sions (1)  that  even  individual  parts  of  the  central  system  are  themselves  in 
a  position  to  function  to  a  certain  extent  independently,  and  (2)  that  even 
the  brain  and  spinal  cord  of  vertebrates  are  composed  of  a  series  of  centers. 
Whether  the  one  or  the  other  of  these  is  more  highly  developed,  whether 
they  are  in  connection  with  deeper  centers,  and  whether  they  have  con- 
nections among  themselves  and  with  higher  centers  determine  the  measure 
of  the  higher  or  lower  development  of  the  central  system.  We  will  find 
later  that,  in  the  course  of  the  development  of  a  class,  individual  centers 
connected  with  the  central  nervous  system  have  reached  a  high  development, 
while  others  have  arrived  at  a  certain  stage  (or  reached  a  certain  type) 
where  they  remain  stationary  and  throughout  all  subsequent  posterity  re- 
main everywhere  alike. 

One  can  conceive  that  in  its  essentials  every  nervous  system  is  com- 
posed of  afferent  tracts  and  efferent  tracts  and  of  tracts  which  form  the 
connections  of  the  elements  among  themselves. 

A  good  insight  into  the  complete  structure  of  a  single  ganglion  may  be 
gained  by  a  study  of  the  opposite  figure  (Fig.  8).  It  represents  the  entire 
first  abdominal  ganglion  of  the  ventral  nerve-cord  of  a  river  cray-fish,  and 
owing  to  the  comparative  simplicity  of  the  relations  permits  an  insight  into 
the  details.  We  have  here  a  sort  of  schema  of  a  central  nervous  system,  and 
gain  at  once  an  outlook  over  an  entire  mechanism  adapted  for  the  exercise 
of  the  functions  of  a  central  organ. 

The  nervous  system  of  a  cray-fish,  like  that  of  all  arthropoda,  consists 
of  a  great  number  of  separate  ganglia,  which  are  united  together  by  longer 
or  shorter  commissures.  From  the  various-sized  nerve-cells  (d,  e,  f)  there 


Fig.  8.— First  abdominal  ganglion  of  the  ventral  nerve-cord  of  Astracus 
fluviatilis.  Living  tissue  stained  with  methyl-blue.  Nervous  tissue  only  is 
stained.  Significance  of  large  fibers  Rf  not  understood,  m  n  o,  Single  cell  from 
the  ganglion.  Periphere  nerven,  Peripheral  nerve.  Einzelne  Zelle  aus  dem  Gang- 
lion, a  single  cell  from  the  ganglion.  Further  description  in  text.  (After  Retzius.) 


28 


ANATOMY   OF   THE    CENTRAL   NERVOUS    SYSTEM. 


arises  always  a  single  immense  branch,  which  after  a  short  course  divides 
into  one  fiber,  which,  at  the  periphery  of  the  ganglion,  passes  out  as  neu- 
raxon,  and  one  fiber,  which  remains  within  the  ganglion,  rapidly  dividing 
into  twigs.  The  neuraxon  passes  either  direct  (Fig.  8,  e)  into  a  nerve,  in 
which  case  it  is  probably  of  motor  nature,  or  it  passes  into  a  commissural 
nerve,  which  joins  with  the  ganglion,  with  those  located . farther  anterior 
or  posterior,  as  is  the  case  with  all  neuraxons  from  the  very  large  cells  (Fig. 
8,  d  and  /  ).  The  neuraxon  may  pass  along  the  same  side  (d)  or  it  may  cross 
over  to  the  opposite  side  (/).  From  the  neuraxon  the  dendrites  branch 


Fig.  9. — From  the  cornu  Ammonis  of  the  rabbit.  A,  Composite  figure  from 
preparations  by  S.  R.  y  Cajal.  a,  b,  c,  Association-cells  whose  long  neuraxons 
split  up  into  moss-like  twigs,  which  invade  the  layer  of  pyramidal  cells  (A). 
At  the  left  is  a  completely-sketched  pyramidal  cell.  Through  its  descending 
neuraxon  it  is  in  relation  with  the  "brain-pith"  and  through  its  ascending  den- 
drites it  is  in  relation  with  other  systems  and  cells  not  figured.  Through  the  asso- 
ciation-cells many  pyramidal  cells  are  brought  into  combination. 


off  and  pass  into  the  substance  of  the  ganglion.  In  their  finer  ramifications 
they  are  well  adapted  to  connect  together  the  separate  elements  of  the 
whole  ganglion. 

In  the  fine  net-work  which  they  form,  appear  nerve-fibers  which  come 
either  from  the  peripheral-sensory  nerves  (2  a),  or  come  from  other  ganglia 


GANGLION-CELL   AND   NERVE.  29 

(I,  i).  Note  that  the  nerve-trunk  (2  a)  contains  nerve-fibers  which  pass  into 
the  ganglion  and  those  which  come  from  other  ganglia  of  the  same  side  or 
the  opposite  side.  How  many  possibilities  of  association  are  given  in  this 
simple  ganglion! 

Every  cell  and  every  fiber  can,  through  the  profuse  terminal  ramifica- 
tion, come  into  relation  with  innumerable  other  cells  and  fibers.  Besides 
that,  most  cells  stand  in  combination  with  tracts  from  distant  centers  and 
also  from  the  periphery. 

There  are  also  cells — already  demonstrated,  at  any  rate,  for  all  classes  of 
vertebrates — which  stand  in  no  direct  relation  to  the  outer  world  and  are 
adapted  only  for  joining  one  central  cell  more  intimately  with  that  of  an- 


I 


Fig.  10. — Isolated  nerve-fibers  from  the  spinal  cord  of  a  dog.  ca,  Axis- 
cylinder,  mg,  Medullary  sheath,  g,  Outer  sheath,  c,  Nucleus  and  protoplasm, 
to  be  seen  occasionally  on  the  surface  of  fibers.  (After  Ranvier.) 


other.  These  cells  are  called  Association-cells.  Such  cells  are  very  widely 
disseminated.  Nowhere  does  their  significance  become  more  readily  clear 
than  in  the  cornu  Ammonis:  a  portion  of  the  olfactory  cortex.  Fig.  9  shows 
a  section  through  this  portion  of  the  cortex. 

Below  the  layer  of  large  pyramidal  cells,  which  make  up  the  principal 
cell-layer  of  this  region,  note  the  small  cells  which  send  their  neuraxons 
near  to  the  pyramidal  cells  or  even  through  the  layer,  after  which  it  divides 
into  fine  transverse  branches,  from  which  great  terminal  ramifications  push 


30  ANATOMY   OF   THE    CENTRAL   NERVOUS    SYSTEM. 

in  between  the  pyramidal  cells  from  above  and  from  below.  These  terminal 
bushes  (Endbaumchen)  are  well  adapted  to  join  together  the  elements  of 
the  layer  in  which  they  terminate. 

The  nerve-fibers  of  the  brain  and  spinal  cord  are  of  very  varying  width 
and  in  grown  mammals  probably  all  are  provided  with  medullary  sheaths. 

Every  nerve-fiber  loses  its  sheath  of  Schwann  where  it  enters  the  central 
system.  Only  a  thin  layer,  present  even  in  peripheral  nerves  and  first  seen 
by  Kanvier,  covers  the  axis-cylinder  within  the  brain  and  spinal  cord. 

These  are  the  elements  from  which  the  central  nervous  system  is 
constructed. 

In  a  general  way,  those  parts  which  are  composed  principally  of 
medullated  nerves  appear  white  (white  substance):  those  in  which  ganglion- 
cells,  axis-cylinders,  and  neuroglia  predominate  appear  gray  (gray  sub- 
stance). The  gray  substance  is  more  vascular  than  the  white. 


CHAPTER    III. 

CEXTBAL   ORGAN  AND  PERIPHERAL  NERVES   (PHYSIOLOGICAL). 

NEXT  to  a  knowledge  of  the  ganglion-cells,  and  of  their  grouping  to 
form  smaller  or  larger  centers,  the  most  important  question  is:  What  is 
known  of  these  cells  physiologically?  And,  first  of  all,  we  know  that  a 
motor  nerve  loses  its  function  when  separated  from  its  cell  of  origin,  and, 
too,  that  destruction  of  gray  matter,  in  which  sensory  fibers  end,  destroys 
their  function  as  well.  We  know,  further,  that,  by  irritation  of  the  cells 
in  which  a  nerve  ends,  we  can  produce  all  the  phenomena  which  are  ordi- 
narily observed  in  the  normal  performance  of  its  function.  This  fact 
alone  has  led  to  the  deduction  that  in  the  ganglion-cells  and  their  inter- 
relationships we  have  the  basis  of  nervous  activity. 

Numerous  experiments  have  demonstrated  that  a  sensory  impression, 
which,  coming  from  the  periphery,  enters  the  nerve-center,  may  there  excite 
cells  of  origin  of  motor  fibers,  and  bring  the  end-organs  of  the  latter,  the 
muscles,  into  activity.  This  process  is  well  known  as  reflex  action.  The 
examination  of  such  reflexes  led  subsequently  to  the  additional  very  inter- 
esting datum,  that  the_sensory  impulse  does  not  always  immediately  excite 
a  motor  discharge,  but  rather  that  a  certain  intensity  of  the  original  irrita- 
tion is  necessary,  although  a  feeble  irritation,  if  continued  for  a  time,  may 
finally  excite  the  motor  apparatus.  The  theory  is  that  ganglion-cells  have 
lli<>  property  of  storing  up  and  retaining  irritations  coming  to  them  until 
the  accumulated  irritation  is  too  great  or  some  new  irritation  arrives  from 
some  other  direction,  when  they  suddenly  discharge. 

The  small  nerve-center  of  the  crab,  already  mentioned  in  Chapter  II, 
receives  many  fibers  from  the  periphery,  and  sends  out,  from  the  large  cells 
it  contains,  large  fibers  to  the  muscles.  A  glance  at  it  and  at  the  accom- 
panying figure  shows  that  a  given  irritation  never  affects  one  cell  only,  but 
rather  that  an  impression,  which  is  conducted  from  one  point  in  the  pe- 
riphery by  a  single  fiber  to  the  nerve-center,  may  there  "charge"  a  large  col- 
lection of  motor-cells.  The  subsequent  discharge  in  like  manner  excites 
not  just  one  motor  fiber,  but,  according  to  the  anatomical  relations  of  the 
motor  cells,  brings  an  entire  system  of  muscles  into  contraction.  In  this 
wise  is  explained  (Exner)  how  a  single  sensory  impression  may  lead  to  a  com- 
plicated movement,  in  which  many  different  muscles  may  take  part.  What 
kind  of  motor  reaction  occurs  from  a  sensory  impulse  depends  upon  which 

(31) 


32  ANATOMY    OF    THE    CENTBAL   NEEVOUS    SYSTEM. 

of  the  sensory  nerves  are  irritated,  and  especially  upon  the  relationship 
between  the  cells  which  form  the  motor  apparatus  excited.  There  is  much 
evidence  in  favor  of  the  view  that  such  relationships,  when  once  established  in 
the  course  of  evolution,  are  afterward  inherited;  so  that  the  structure  of  a 
single  nerve-center  is  practically  the  same  for  each  individual,  and  that, 
through  this  inherited  apparatus,  numerous  apparently  complicated  actions 
are  made  possible  once  for  all.  But  there  are  experiences  which  teach  that 


11. — Schema  of  a  very  simply  constructed  nervous  apparatus,  com-, 
prising  motor  and  sensory  nerve  and  center;  adapted  for  explaining  the  simplest 
reflexes.  8,  Sensory  cell  whose  dendrite  brings  to  it  impressions  from  the  skin, 
while  its  neurite,  or  neuraxon,  passes  to  the  nerve-center,  where  it  influences  M 
and  A.  M,  Motor  cell  for  the  upper  muscle.  A,  Association-cell  which  transmits 
stimuli  received  by  S  on  to  M',  where  it  takes  effect  either  simultaneously  or 
subsequently.  M',  Motor  cell  for  the  lower  muscle. 


in  certain  portions  of  the  nervous  system  constantly  new  associations  are 
being  formed  ~by  exercise.  The  central  nervous  system  would,  then,  consist 
of  one  part,  which  is  congenital  and  arises  from  the  primordial  racial  exercise 


CENTEAL    ORGAN   AND    PERIPHEHAL    NERVES    (PHYSIOLOGICAL).  33 

(phylogenetic),  and  of  other  parts  which,  only  by  use  during  the  person's 
life,  derive  their  relationships  (ontogenetic). 

Congenital  mechanisms  are  found  in  all  parts  of  the  nervous  system, 
but  observation  of  movements  of  embryos  and  infants  shows  that,  at  least 
in  respect  to  the  nervous  apparatus  connected  with  the  vegetative  functions, 
as  in  the  sympathetic  and  in  the  large  territory  of  the  spinal  cord  and  the 
bulb,  such  mechanisms  predominate.  Probably  to  these  may  be  added  a 
large  part  of  the  midbrain  and  cerebellum.  Comparative  anatomy  teaches 
that,  up  to  the  higher  mammals,  the  apparatus  lying  anterior  to  these  parts 
are  capable  of  still  greater  variations;  and  observation  of  the  cerebral  cortex 
in  its  particular  development  specially  shows  that  here,  in  cases  of  indi- 
viduals, new  paths  may,  by  practice,  become  fixed. 

In  so  far  as  motor  phenomena  are  considered  as  the  result  of  irritations, 
the  necessary  apparatus  is  called  the  movement-complex.  This  word  was 
coined  by  Exner,  to  whom  we  are  indebted  for  an  excellent  review  of  many 
of  the  related  facts.  One  should  not  imagine,  however,  such  collections  of 
ganglion-cells  as  entirely  simple.  The  majority  of  movements  require  some 
time  for  their  execution,  during  which  numerous  other  muscles  may  come 
into  play  besides  those  first  concerned.  There  must,  therefore,  be  paths 
leading  from  one  collection  of  cells  to  another,  the  latter  group  being 
affected  by  the  irritation  only  when  the  action  of  the  former  is  ended. 

Such  processes  are  known  (Exner)  as  successive  movement-complexes. 
Exner  determined  from  physiological  observations  that,  when  one  searches 
carefully  the  nervous  system  of  the  invertebrates,  one  may  easily  find 
anatomical  series,  which,  once  meeting  with  an  irritation,  may  discharge 
successive  movements  in  perfect  order.  Especially  the  nervous  system  of 
annulata — for  example,  the  earth-worm,  which  we  understand  well  since 
the  excellent  researches  of  Eetzius — shows  how,  from  afferent  sensory  fibers, 
first  a  single  motor  cell-group  is  set  in  action,  and  then,  through  the  proc- 
esses of  large  association-cells,  the  impulse  may  be  transmitted  to  the  next 
ganglion  (Fig.  12).  Besides,  every  ganglion  contains  other  motor  cells 
whose  neuraxons  do  not  connect  with  the  nerves  of  the  corresponding  meta- 
mere,  but  which  end  in  muscles  that  are  anterior  or  posterior  to  this.  So  an 
impression,  which  is  received  by  an  animal  in  any  part  of  its  body-surface, 
may  bring  into  action  first  the  muscles  of  that  part,  and  then  also  those  of 
metameres  lying  anterior  or  posterior  to  it.  When  such  a  successive  move- 
ment has  once  begun,  another  element  enters  in  to  regulate  it.  With  the 
changing  position  of  the  muscles  and  limbs,  change  also  the  sensory  im- 
pressions received  by  them.  Consider  the  above-mentioned  earth-worm. 
The  muscles  of  the  first  metamere  contract  from  irritation  of  the  apparatus 
of  touch;  perhaps,  too,  those  of  the  second.  But  by  reason  of  these  con* 
tractions  other  portions  of  the  integument  come  into  contact  with  the 


34 


ANATOMY    OF    THE    CENTRAL   NERVOUS    SYSTEM. 


ground;  new  impulses  are  excited,  which  pass  to  still  other  ganglia;  and  in 
this  way  the  contractions  may  extend  to  include  farther  metameres;  in 
short,  an  irritation  affecting  one  portion  of  the  worm's  body,  provided  there 


Fig.  12. — Several  ganglia  from  the  ventral  cord  of  an  earth-worm, — Lum- 
"bricus  terrestris, — showing  the  elements  for  successive  movement-combinations. 
(After  Retzius.) 


is  the  necessary  co-ordination  of  movements  present,  brings  the  whole 
animal,  in  a  purely  reflex  way,  into  motion, — crawling.    Indeed,  this  crawl- 


CENTRAL    ORGAN    AND    PERIPHERAL    NERVES    (PHYSIOLOGICAL).  35 

ing  may  give  the  impression  of  an  extreme  effect  in  proportion  to  the 
irritation.  If  one  turns  a  sea-urchin  on  its  back,  it  begins  at  once  to  lay 
hold  of  the  ground  with  the  long  suckers  which  cover  its  whole  body. 
Each  arm,  however,  contracts  instantly,  when  it  touches  the  ground.  The 
almost  egg-shaped  animal  is  thereby  more  closely  drawn  to  the  ground. 
Then  a  peculiar  thing  happens,  as  Eomanes  and  Ewart  have  well  described. 
At  one  place,  no  matter  which,  apparently,  the  arms  are  more  strongly  con- 
tracted. Immediately  all  the  others  lose  their  hold,  and  the  animal  turns 
toward  that  side  where  the  stronger  contraction  occurred.  As  a  result  of 
this,  other  arms  are  brought  into  contact  with  the  ground,  and  they  contract 
in  turn,  and  the  process  is  repeated  until  the  sea-urchin  stands  upon  edge, 
and  then  new  pedicels  come  into  action  and  finally  bring  the  animal  into 
its  normal  position.  Here  we  have  a  purposive  movement,  apparently  prac- 
ticable only  through  minute  care  and  reflection,  which  may  be  explained 
by  simple  reflex  processes:  by  the  contraction  in  the  muscles  of  the  am- 
bulacral  feet  following  excitation  of  their  sensory  nerves.  That  the  move- 
ment is  a  regulated  one  bespeaks  a  combination  of  the  nerves  of  the  am- 
bulacral  feet.  But  in  this  simple  experiment  appears  a  new  faculty,  which 
until  now  we  have  not  mentioned  among  the  properties  of  the  central  nerv- 
ous apparatus:  the  cessation  of  motion  when  once  the  animal  reaches  a 
position  of  rest.  There  must  here  be  introduced  an  inhibition  from  the 
center,  otherwise  one  could  not  understand  why  the  sea-urchin  should  not 
keep  on  turning  until  tired  out,  since  even  in  the  normal  position  new  arms 
are  always  coming  in  contact  with  the  ground.  In  fact,  it  is  a  property  of 
nerve-centers,  everywhere  recognized,  that  they  are  not  only  able  to  excite 
movements,  but  also  to  prevent  them.  The  mechanism  is  not  yet  clearly 
understood.  Doubtless  such  inhibitions  are  propagated,  as  are  the  move- 
ments, from  the  ganglion  first  excited  to  the  others. 

It  would  be  very  alluring  to  follow  from  these  first  ideas  further  along 
the  events  in  a  given  part  of  the  nervous  system,  or  to  see  what  takes 
place  in  the  internal  nervous  arrangement  in  the  production  of  a  given 
complicated  action.  However  simple,  though,  may  be  the  most  primitive 
nervous  apparatus,  regarded  anatomically,  such  views  are  misleading. 

As  the  simplest  central  nervous  arrangement,  we  can  consider  that 
which  is  made  up  of  centripetal  sensory  and  centrifugal  motor  fibers,  in 
which  it  is  agreed  that  the  ends  of  the  sensory  nerve  are  in  contact  directly, 
or  through  the  mediation  of  a  second  cell,  with  the  cell  of  origin  of  the 
motor  nerve.  Such  simple  combinations  are  widely  found  in  the  inverte- 
brates as  well  as  in  the  vertebrates.  They  occur  partly  in  the  sympathetic 
ganglia,  partly  also  as  direct  reflex-paths  in  the  central  nervous  system. 
Absolutely  isolated,  simple  reflex-centers  are  not  yet  known,  but  even  the 
smallest  are  in  connection  with  others  similar  to  them.  Such  a  center  is 


36 


ANATOMY    OF   THE    CENTRAL    NERVOUS    SYSTEM. 


seen  in  Fig.  11.  But  all  the  cells  are  only  slightly  dependent  on  each 
other,  being,  for  a  large  part  of  their  function,  wholly  independent.  As  an 
example  of  such  isolated  reflex  action,  we  have  the  movements  occurring  in 
the  musculature  of  a  portion  of  the  intestines  removed  from  the  body,  which 
take  place  with  entire  regularity,  when  irritated  on  its  mucous  membrane. 
The  influence  on  these  short  reflex-arcs,  which  larger  and  more  extensive 
arcs  have,  is  well  known;  such,  for  example,  as  those  passing  through  the 
sympathetic  ganglia  and  the  spinal  nerve-roots.  These  form  new  neurons, 
which  are  connected  with  those  of  the  intestines,  influencing,  exciting,  and 
restraining  them. 

THE   PERIPHERAL   NERVES. 

All  examinations  of  the  vertebrates  have  shown  that  the  motor  nerve 
arises  from  a  large  ganglion-cell,  which  sends  out  its  neuraxon  to  a  muscle. 


Raducant. 


Fig.  13.— Section  of  the  spinal  cord  of  a  human  embryo  of  the  fourth  week. 
Note  ventrally  the  anterior  or  motor  root  developing  from  cells  of  the  cord.  In 
the  dorsal  portion  (four  and  one-half  weeks)  the  sensory  root  grows  in  from  cells 
of  the  spinal  ganglion.  (Combined  from  figures  by  His.) 


where  it  ends  by  division.  Everything  that  has  been  observed  with  in- 
vertebrates indicates  that  there,  also,  this  is  the  case.  On  the  other  hand, 
with  invertebrates  the  direct  observation  has  been  made  of  nerve-fibers 
originating  in  cells  in  the  skin,  sensory  nerves,  passing  into  the  central 
organ,  and  there  ending  by  free  extremities.  His  has  made  valuable  ex- 
aminations along  this  line  with  vertebrates  (Fig.  13). 

In  embryos  of  vertebrates  the  central  nervous  system,  as  is  well  known, 
presents,  in  the  early  stages  of  development,  a  canal.    His  determined  that 


CENTRAL    ORGAX   AXD    PERIPHERAL    XERYES    (PHYSIOLOGICAL).  37 

the  fibers  of  the  peripheral  nerves  have  two  quite-different  origins.  All 
motor  fibers  arise  as  axis-cylinder  processes,  or  neuraxons,  from  the  cells 
lying  in  the  ventral  portion  of  this  canal.  Each  cell  sends  out  a  fibril 
toward  the  surface,  and  there  the  fibrils  approximate  each  other  to  form 
ventral  nerve-roots.  The  sensory  root-fibers,  which  arise  mainly  dorsal,  have 
an  entirely  different  beginning.  They  proceed  from  the  ganglia  which 
lie  near  the  cord  throughout  its  length,  and  not  from  within  the  cord  itself. 
From  the  cells  of  these  ganglia  (spinal  ganglia  and  ganglia  of  the  cranial 
nerves)  fibers  grow  in  two  directions.  One  set  enters  the  central  organ, 
the  other  grows  toward  the  periphery  as  sensory  nerves. 

In  the  vertebrates  the  cells  of  origin  of  most  motor  nerves,  especially 
those  supplying  striated  muscle,  are  in  the  central  axis.  They  have  already 
been  considered  as  forming  good  examples  of  the  superposition  of  different 
neurons.  But  not  all  of  the  motor  nerves  arise  in  this  way.  Scattered 
throughout  the  body  we  find  ganglion-cells,  whose  axones  end  in  the  non- 
striated  muscle-fibers  of  the  blood-vessels,  the  intestines,  the  heart,  and 
other  viscera.  These  cells,  usually  classed  as  belonging  to  the  sympathetic, 
must  be  regarded  as  motor  cells,  because  on  their  normal  supply  depends 
the  inherent  power  of  contraction  which  these  organs  possess.  They  lie  in 
many  locations — for  instance,  in  the  intestinal  walls  and  the  heart — in 
relatively  close  contact  with  other  axones  which  arise  from  other  places,  as 
from  the  spinal  cord,  etc.  Here,  too,  then,  in  the  sympathetic  there  are 
motor  paths  of  different  orders.  We  have  seen  that  in  mammals  a  large 
share  of  the  secondary  motor  paths  reach,  in  some  way,  to  the  organs  of 
consciousness.  That  is  not  true  of  all  these  tracts.  It  is  better  to  consider 
the  motor  centers,  the  central  and  peripheral  sympathetic  as  capable  of  in- 
dependent action,  and  to  determine  in  each  case  how  far  higher  nerve-tracts 
associate  themselves  to  these,  and  how  far  higher  nerve-centers  can  affect 
their  action.  With  mammals  all  the  striated  muscles  are  innervated  from 
the  central  organs,  and  only  the  smooth  muscles,  as  well  as  those  of  the 
heart,  are  to  some  extent  independent  of  them;  but  with  the  lower  animals 
there  are  also,  in  the  periphery,  many  ganglion-cells  for  voluntary  muscles. 

The  sensory  nerves  in  vertebrates  are  mainly  outgrowths  from  the 
cells  of  the  spinal  ganglia.  They  also  split  up  when  they  arrive  at  the  pe- 
riphery, and  end  either  freely  in  the  epithelium  or  in  some  modified 
end-apparatus,  usually  an  epithelial  structure.  Aside  from  the  ontogeny 
of  the  sensory  nerves,  much  of  interest  is  known  of  their  phylogeny. 
As  is  well-known,  the  outer  covering  of  slightly-developed  animals,  as  the 
ccelenterates,  among  the  ordinary  epithelial  cells,  presents  still  others 
characterized  by  their  arrangement  in  groups  and  by  the  possession  of 
a  long  end-filament,  which  sinks  into  the  nervous  system.  In  the  whole 
list  of  lower  animals  it  is  a  frequent  occurrence  that  cells  lying  in  the 


88 


ANATOMY    OF   THE    CENTRAL   NERVOUS    SYSTEM. 


Fig.  14. — Schema  of  the  peripheral  and  central  nervous  system.  The  rela- 
tions shown  do  not  exist  in  any  particular  animal,  but  represent  rather  the 
principles  determined  from  a  comparative  study  of  many  animals,  and  are  in- 
troduced for  the  elucidation  of  the  text.  Note  the  motor  and  sensory  nerves, 
peripherally  and  centrally  located  centers,  and  the  connections  represented.  A, 
B,  C,  and  D  indicate  that  the  tract  is  one  of  I,  II,  III,  or  IV  order,  respectively. 


CENTRAL   ORGAN   AND   PERIPHERAL   NERVES    (PHYSIOLOGICAL).  39 

ectoderm  are  joined  to  the  neighboring  nerve-centers  by  such  fibers.  Their 
position  in  the  epidermis  indicates  that  this  is  a  part  of  the  sensory  ap- 
paratus, and  all  doubts  about  this  being  true  disappear  when  one  recog- 
nizes how  frequently  these  cells  are  in  relation  with  structures  adapted  to 
the  reception  of  special  impressions.  Long,  stiff  hairs,  swinging  brushes, 
projecting  horns,  seem  easily  able  to  communicate  tactile  impressions,  while 
one  may  find  analogous  cells  arranged  to  form  the  walls  of  a  cavity,  in 
which  a  pebble,  an  otolith  swinging  inside  the  cavity,  represents  the  sensory 
apparatus  for  maintaining  the  equilibrium.  Lentiform  parts  of  the  ecto- 
derm lie  in  other  places  in  front  of  such  cells,  and  are  well  adapted  to 
transmit  rays  of  light  or  heat  to  these  cells  in  a  peculiar  manner.  It  would 
scarcely  be  possible  to  describe  all  the  manifold  arrangements  which  func- 
tion as  sensory  mechanisms  in  the  invertebrates,  but  it  must  be  emphasized 
that  between  the  simple  epithelial  cell  of  the  ectoderm  and  the  highly 
differentiated  apparatus  are  found  all  transitional  forms,  and  that  in  the 
most  highly  developed  this  same  type,  the  epithelial  cell  with  a  filament 
extending  inward  to  the  nervous  system,  reappears.  There  is  one  place 
where  one  may  find  a  large  number  of  intermediate  forms  in  a  limited  space, 
ranging  from  a  simple  epithelial  cell  connected  with  the  nerves  up  to  the 
more  complicated  sense-hillocks.  It  is  the  skin  of  a  transparent  snail,  the 
pterotrachea.  The  connection  of  epithelial  cells  with  nerves  leading  to  the 
central  organ,  in  the  angle-worm,  has  been  well-described  by  Lenhossek 
during  the  last  few  years.  Eesearches  of  my  own  and  those  of  Eetzius  have 
fully  confirmed  his  reports.  From  numerous  cells  of  the  integument  are 
seen  delicate  fibrils  arising,  which  extend  to  nerve-centers  and  there  ter- 
minate by  division.  Lenhossek  has  formulated  an  hypothesis  which  has 
proved  to  be  of  great  worth  as  a  working-basis,  and  bids  fair  to  simplify  and 
extend  our  knowledge  of  the  peripheral  sensory  nervous  system.  According 
to  him,  all  sensory  nerves,  in  the  invertebrates  as  well  as  in  vertebrates,  arise 
from  such  cells  that  are  originally  in  the  integument.  ^The_cells  recede 
deeper  and  deeper,  leaving  behind  a  long  and  often  branched  fiJament  in 
the  skin.  In  the  vertebrates  they  extend  as  far  as  the  vertebral  column, 
forming  the  spinal  ganglia.  Whether  the  cells  Ire  immediately  in  the 
surface-epithelium  or  are  connected  with  it  by  their  processes,  the  sensory 
nerves,  they  invariably  send  one  filament  back  into  the  central  organ. 
Eetzius  has  described  such  transition  cell-forms  in  mollusks,  the  peripheral 
filaments  being  of  different  lengths,  where  the  ganglion-cells,  corresponding 
to  epithelial  cells,  are  often  found  not  in  the  skin  itself,  but  under  it  at 
various  levels.  In  Fig  15  is  represented,  after  drawings  of  Eetzius,  a  scheme 
aiding  one  to  connect  the  foregoing  with  the  development  of  the  sensory 
nervous  system. 

It  is  not  only  in  the  lower  animals  that  the  sensory  end-cells  are  met 


40 


ANATOMY    OF   THE    CENTKAL    XEKVOUS    SYSTEM. 


with  in  the  periphery;  they  are  similarly  found  in  the  vertebrates,  and  in 
many  different  forms,  as  is  the  case  in  the  nerve-endings  of  the  sense-organs. 
The  epithelium  of  the  nasal  mucous  membrane,  like  that  of  the  angle-worm, 
sends  only  one  process  back  into  the  brain;  but  in  the  ear  there  are  no 
end-cells  in  this  sense,  the  corresponding  cells  lying  in  the  spinal  ganglion 
of  the  cochlea,  while  their  branched  peripheral  processes  surround  the  hair- 
cells  of  the  crista  acustica,  or  of  the  organ  of  Corti,  after  the  manner  of 
the  sensory  nerve  with  the  epiderpis-cell  (Fig.  16).  So  also  with  the  taste- 
fibers  has  such  a  branching  around  cells  been  determined.  In  the  retina, 
we  know,  there  are  nerve-fibers  which  come  from  the  brain  and  arborize 


Fig.  15. — a,  Sensory  epithelium  of  the  earth-worm.  6,  Sensory  epithelium 
of  the  snail,  c,  Spinal  ganglion-cells  of  a  vertebrate.  (After  Retzius.) 

[One  process  of  the  cell  (c)  extends  to  the  skin  as  a  sensory  nerve-fiber; 
it  is  the  homologue  of  the  dendrite,  but  in  this  situation  is  structurally  modified 
into  a  typical  axis-cylinder.  One  process  extends  into  the  central  nervous  sys- 
tem, and  is  the  efferent  neuraxon,  axone,  or  neurite,  also  here  having  the  structure 
of  a  typical  axis-cylinder.  Such  cells  have  been  called  bipolar,  because  they 
possess  two  axis- cylinders;  inasmuch,  however,  as  they  possess  but  one  neuraxon, 
the  utility  of  the  term  bipolar  might  be  called  in  question. — W.  S.  H.] 


around  their  respective  cells,  while  there  are  also  ganglion-cells  in  it,  whose 
axones  pass  backward  into  the  brain. 

Sensory  nerves  are  widely  distributed  over  the  entire  body.  They  are 
located  not  only  in  those  places  usually  known  to  be  sensitive,  but  also  in  all 
other  tissues  and  organs.  Whether  one  examine  the  liver  or  the  kidney,  the 


CENTRAL    ORGAX   AXD    PERIPHERAL    XERYES    (PHYSIOLOGICAL).          41 

lungs  or  the  wall  of  a  blood-vessel,  one  always  finds  delicate  nerve-arbor- 
izations in  unsuspected  numbers.  A  large  portion  of  them  end  probably 
in  the  peripherally  placed  sensory  end-cells  belonging  to  the  reflex-arc  of 
the  sympathetic;  another  portion  may  very  probably  be  traced  to  the  spinal 
ganglia  and  even  to  the  spinal  cord  itself.  Especially  the  investigations  of 
the  last  few  years,  making  use  of  the  silver  and  methyl-blue  stains,  have 
not  only  disclosed  the  wealth  of  nerves  in  the  different  organs,  but  have  also 
shown  that  we  have  regarded  the  sensory  innervation  of  the  sensitive  sur- 
faces, as  the  skin  and  the  gustatory  mucous  membrane,  as  much  less  fully 


Fig.  16. — a,  Sensory  epithelium  of  the  nose  sending  the  neuraxon  as  fila 
olfactoria,  or  olfactory  nerve,  backward  into  the  brain,  where  it  breaks  up  into 
branches.  The  neuraxon  is,  in  this  situation,  a  non-medullated  axis-cylinder. 
The  dendrite  is  represented  by  the  distal  process  of  the  specialized  olfactory  cell. 
6,  Cell  from  the  Ganglion  spirale  of  the  cochlea;  the  dendrite  passes  from  its 
peripheral  arborization  around  the  bristled  cells  of  the  macula,  or  hair-cells  of 
the  organ  of  Corti  direct  to  the  ganglion-cell,  whence  the  neuraxon  passes  as 
Ramus  cochlearis  Nervi  acustici  toward  the  brain.  (After  Eetzius.) 


supplied  than  they  really  are.  One  finds  there  enormous  plexuses  of  nerve- 
fibers  beneath  and  between  the  epithelial  cells,  and  they  send  one,  often 
many,  fine  fibrils  to  each  cell.  Fig.  17  indicates,  for  example,  how  surround- 
ing every  hair  there  lies  a  veritable  crown  of  nerve-fibrils  (.4  and  B],  how 


42  ANATOMY    OF    THE    CENTRAL    NERVOUS    SYSTEM. 

to  the  epithelial  cells  of  a  frog's  gum  there  pass  end-fibers  (C),  and  how  the 
pigment-cells  in  the  skin  of  fishes  are  densely  surrounded  by  a  regular  net 
of  fibers  (D).  In  the  liver,  too,  and  the  bladder,  and  in  many  other  places, 
one  can  find  numerous  examples  of  the  abundant  peripheral  innervation. 
We  have  always  attached  too  great  importance  to  the  single  end-apparatus, 


Fig.  17. — A,  Hairs  from  a  mouse.  B,  Cross-section  of  same.  (V.  Gehuchten.) 
C,  Nerves  to  the  epithelial  cells  of  a  frog's  gums  (Gingiva).  Methyl-blue  prepa- 
ration by  Berthi.  D,  Pigment-cells  from  the  skin  of  Alburnus,  showing  the  nerve- 
reticulum.  (Berthi  and  Bunge.) 

overlooking  the  fact  that  really  the  major  portion  of  the  body-tissues  is 
supplied  with  nerves  for  even;  _cell.  One  can  hardly  overestimate  the 
wealth  of  nerve-fibers  in  the  real  end-organs  themselves,  as  the  taste- 


CENTRAL    ORGAN   AND    PERIPHERAL    NERVES    (PHYSIOLOGICAL).          43 

papillae  and  the  tactile  papillae.  Good  staining  discloses  with  each  of  them 
plexuses  of  unsuspected  density  of  arborization. 

For  what  services  may  such  an  abundant  sensory  innervation  be  pro- 
vided? It  occurs  immediately  to  one  that  there  is  a  great  number  of  re- 
flexes, very  necessary  to  the  preservation  of  the  individual,  even  though  he 
be  unaware  of  them.  The  regulation  of  the  secretions,  the  blood-supply 
to  the  skin  in  relation  to  the  caloric  body-economy  of  the  organism,  the 
adjustment  to  varying  illumination,  the  tension  of  the  muscles  and  tendons 
through  the  respective  tendon-reflexes,  the  different  response  by  such  vary- 
ing tensions  according  to  the  intensity  of  the  voluntary  impulse,  and  many 
other  phenomena  could  be  cited.  To  all  of  them  is  necessary,  besides  the 
motor  part  of  the  reflex-arc,  a  sensory  part.  Indeed,  Exner,  to  whom  we  are 
indebted  for  indicating  the  importance  of  these  short  reflex-arcs  and  the 
roles  they  play  in  the  organism,  has  pointed  out  how,  in  general,  for  the 
production  of  any  movement  the  sensory  innervation  must  ~be  intact.  The 
act  of  swallowing,  for  example,  divides  into  a  voluntary  and  a  reflex  act. 
Anaesthetize  the  pharynx  with  cocaine,  and  the  ability  to  perform  the  volun- 
tary part  of  swallowing  is  preserved;  the  bolus,  however,  on  reaching  the 
oesophagus,  produces  no  impression  on  it,  and  the  reflex  part  of  the  act  is 
lost.  Here,  then,  is  the  reason  why  the  mucous  membrane  of  the  gullet 
possesses  such  an  apparently  superfluous  sensory  innervation,  and  why,  be- 
neath and  in  its  epithelium,  there  lie  such  great  plexuses  of  nerve-fibers. 
Another  good  example  of  the  importance  of  sensory  regulation  of  purely 
motor  phenomena  is  offered  by  the  movements  of  the  fingers.  These  move- 
ments are  much  impaired — the  "fingers  are  stiff" — when  sensory  dis- 
turbances alone  are  present  in  the  hand.  This  can  be  brought  about  arti- 
ficially. Let  the  hand  become  too  cold,  and  it  becomes  stiff;  i.e.,  cannot 
move  well,  even  in  those  movements  depending  upon  the  muscles  lying  in 
the  protected  forearm.  These  latter  muscles  cannot  contract  normally,  it 
appears,  when  no  regulating  impressions  arrive  from  the  tendon  and  joint 
nerve-endings.  The  stiff  fingers,  which  one  experiences  often  on  a  winter's 
walk,  are  due  to  the  presence  of  "  Senso-mobility."  Probably  many  motor 
disturbances  of  hysteria  are  of  this  category. 

An  abundant  sensory  innervation  is,  therefore,  necessary,  not  only  for 
countless  reflex  actions,  but  for  the  regulation  of  many  seemingly  purely 
voluntary  movements,  as  well. 

By  "sensory  innervation,"  however,  one  must  not  think  only  those  proc- 
esses are  meant  which  enter  into  our  consciousness,  but  rather  all  those  by 
which  from  any  place  in  the  body  impressions  are  conducted  to  the  nearest 
ganglion  or  to  the  central  axis.  Whether  they  be  conducted  farther  still, 
or  whether  they  be  recognized  by  the  individual  as  they  occur,  does  not 
effect  their  nature.  Sensation  and  perception  are  not  the  same  thing. 


44  ANATOMY    OF   THE    CENTRAL   NERVOUS    SYSTEM. 

The  most  manifold  tracts  and  centers  serve  sensibility,  and  in  verte- 
brates, especially  in  man,  who  is  able  to  give  information  in  regard  to  the 
perception  of  certain  impressions,  we  have  found  a  multiplicity  of  sensations. 

The  sensory  control  required  by  apparently  similar  movements  is  not 
always  the  same.  Particularly  in  the  higher  animals  there  seem  to  be 
more  factors  entering  into  this  control  than  in  the  lower  ones.  But  even 
mammals  may,  at  times,  through  habit,  etc.,  learn  to  dispense  with  one  or 
another  such  factor;  i.e.,  may  be  successful  in  performing  acts  through  the 
agency  of  elements  which  in  lower  stages  of  evolution  were  simply  regulative 
in  their  action. 

The  importance  of  the  single  forms  of  this  sensory  regulation  of  en- 
tirely elementary  motor  mechanisms  is  well  illustrated  by  the  shrewd  ex- 
periment of  J.  Eichard  Ewald.  If  one  remove  the  labyrinth  on  both  sides 
of  a  dog,  the  general  muscular  tone,  and  with  it  the  power  to  maintain  the 
vertical  equilibrium,  suffers  so  as  to  render  walking  and  standing  impossible. 
But  this  is  gradually  recovered  from,  the  tracts  for  tactile  and  other  im- 
pressions making  up  for  the  loss.  Remove  now  both  the  cortical  motor 
areas  for  the  legs,  and  the  severe  motor  disturbance  reappears,  the  animal 
cannot  produce  co-ordinated,  or,  indeed,  any  regular  movements.  Still, 
here  follows  slowly  a  recovery.  But  the  dog  is  in  a  serious  state,  being  re- 
duced to  visual  control  for  all  his  movements.  When  the  room  is  darkened, 
or  his  eyes  are  bandaged,  he  falls  helplessly  to  the  ground. 

Lower  vertebrates — frogs,  for  example — cannot  conceal  the  loss  follow- 
ing removal  of  the  labyrinths,  because  with  them  the  possibility  of  substi- 
tuting other  forms  of  sensation  from  the  cerebral  cortex  for  those  lost  is 
very  slight.  They  remain  unable  to  jump  after  removal  of  the  labyrinth. 

The  foregoing  shows  how  complicated,  even  in  the  most  ordinary  act, 
the  mechanism  required  for  its  performance  is.  By  study  and  experimenta- 
tion, one  may,  perhaps,  recognize  in  the  central  organ  at  least  enough  of 
this  mechanism  to  serve  in  explaining  physiological  and  psychological 
processes. 


PART  II. 


REVIEW  OF  THE  EMBRYOLOGY  AND  THE 

COMPARATIVE  ANATOMY  OF  THE 

VERTEBRATE  BRAIN. 


(45) 


CHAPTER    IV. 
THE  DEVELOPMENT  OF  THE  BRAIN  AND  OF   GANGLIA. 

FROM  the  preceding  chapters  we  learn  that  there  are  scattered  ganglia 
with  motor  and  sensory  parts;  but  among  the  higher  animals  the  greater 
part  of  the  central  nervous  system  is  more  or  less  concentrated  into  a  definite 
location.  Among  vertebrates  this  concentrated  nervous  system  includes  a 
longitudinal  cord — the  spinal  cord — into  which  the  sensory  nerves  come 
from  without,  while  from  cells  which  lie  in  the  cord  itself  the  motor  nerves 
arise.  Those  portions  of  the  central  system  which  receive  or  send  out 
numerous  large  nerve-trunks  in  a  relatively  short  space  are  much  thickened. 
As  examples,  one  may  cite  the  cervical  and  lumbar  portions  of  the  spinal 
cord.  This  is  especially  the  case  in  the  cephalic  parts  of  the  animal.  In 
consequence  of  this  all  of  the  craniata  possess  in  this  segment  of  the  system 
an  enlargement, — the  medulla  oblongata.  From  this  arise  the  nerves  for 
the  branchial  arches  and  for  all  the  structures  derived  from  them. 

Another  enlargement  lies  farther  forward  where  in  nearly  all  animals 
large  optic  nerves  enter.  Finally,  one  regularly  finds  at  the  extreme  an- 
terior end  of  the  central  nervous  system  a  usually-large  projection  where  the 
olfactory  nerve  takes  origin. 

In  the  spinal  cord  as  well  as  anterior  to  it  there  exist  connections  of 
one  level  with  another.  These  produce  further  enlargements  of  the  central 
system. 

Finally,  with  the  system  as  just  described  there  are  associated  other 
structures  which  are  not  in  direct  relation  to  the  different  nerves,  but 
which  may  be,  indeed,  very  important  for  certain  functions  of  the  animal. 
For  example,  one  finds,  dorsal  to  the  medulla  in  all  craniata,  a  more  or 
less  fully  developed  cerebellum.  Ventral  and  anterior  to  the  deep  origin  of 
the  optics  is  an  important  apparatus, — the  midbrain-base  with  the  midbrain- 
ganglia, — which  receives  tracts  from  before  and  behind  and  which  also 
sends  out  tracts.  Finally,  there  is  always  developed  anterior  to  the  Thal- 
amencephalon  and  dorsal  to  the  deep  origin  of  the  olfactory  nerve  the  basal 
ganglion  of  the  forebrain, — the  corpus  striatum, — with  which  a  brain- 
mantel  may  be  associated. 

As  is  well  known,  the  spinal  cord  is  alone  sufficient  to  make  the  lower 
vertebrates  capable  of  relatively  complicated  acts. 

One  is  able  to  determine  anatomically  and  even  experimentally  how 

(47) 


48 


ANATOMY    OF    THE    CENTRAL    NERVOUS    SYSTEM. 


the  different  brain-structures  in  the  animal  series  were  added  to  the  spinal 
•cord,  essentially  increasing  the  capability  of  the  organism. 

The  amphioxus  practically  possesses  only  the  spinal  cord,  corresponding 
to  the  metameres,  which  receives  and  gives  off  nerves.  Whatever  brain- 
structures  it  may  have  are  so  small  that  the  investigations  of  our  best  men, 
-covering  several  decades,  have  only  recently — through  Kupffer — succeeded 
in  finding  them.  The  brain-segments  of  the  nervous  system  of  amphioxus 
has  as  yet  remained  quite  refractory  to  physiological  experiments.  A  de- 
capitated amphioxus  conducts  himself  just  like  one  which  still  possesses  the 


Fig.  18. — Sagittal  section  through  the  brain  of  a  four-months'  larval 
sturgeon.     (After  von  Kupffer.) 

pointed  anterior  end  of  the  head  (Steiner).  However,  all  craniate  verte- 
brates possess,  anterior  to  the  spinal  cord,  at  least  the  brain-structures  above 
mentioned.  In  the  field  of  morphology  one  would  hardly  find  anything 
more  interesting  or  instructive  than  a  glimpse  of  the  development  of  the 
brain;  of  the  progressive  or  retrogressive  development  of  particular  parts; 
of  the  development  of  higher  structures  from  parts  which  in  other  animals 
still  exist  as  simple  cuticle.  Let  us  now  become  acquainted  with  these 
processes  step  by  step, — and  see  how  the  whole  was  gradually  built  up,  how 
it  came  to  be  and  how  it  is  ever  changing, — here  increasing  and  there- 
decreasing. 


DEVELOPMENT    OF    THE    BRAIX   AND    GAXGLIA.  49 

Physiologically  these  things  afford  an  especial  interest,  and  it  is  to  be 
hoped  that  they  will  some  time  afford  also  an  especial  interest  psycholog- 
ically. It  is  certainly  to  be  regretted  that  these  subjects  are  here  still  quite 
insufficiently  recognized. 

From  the  foregoing  chapters  we  know  that  the  entire  fundament  of  the 
nervous  system  is  furnished  by  the  outer  germ-layer, — epiblast, — that  this 
fundament  forms  a  plate  which  soon  sinks  in  to  form  a  groove.  Very  early 
the  medullary  groove  becomes  closed,  forming  a  medullary  canal.  But  even 
before  this  closure  is  complete  one  may  recognize  in  all  vertebrates,  in  the 
region  where  the  brain  is  developing,  three  vesicular  expansions:  the 
(primitive)  f  orebrain,  midbrain,  and  hindbrain. 

The  wall  which  closes  the  forebrain  anteriorly  is  called  the  embryonic 
terminal  lamina')  the  closure  of  the  original  medullary  plate  results  in  a 
e earn,  or  raphe. 


Fig.  19. — Longitudinal  section  through  the  brain  of  a  newborn  kitten.  The 
Thalamus  (Zwischenhirn)  and  Corpora  Quadrigemina  (Mittlehirn)  covered  by  the 
Cerebrum  (Vorherhirn) . 


The  section  of  the  brain  of  a  larval  sturgeon  (see  Fig.  18)  contains,  as 
the  description  will  show,  the  most  varied  fundaments  for  the  further  de- 
velopment of  the  separate  brain-segments.  Not  all  come  to  maturity;  many 
remain  in  the  stage  here  shown;  but  among  the  higher  vertebrates  the 
separate  smaller  segments  of  the  brain-tube  become  metamorphosed  into  im- 
portant structures,  whose  development  may  be  very  different  for  the  differ- 
ent classes. 

First  note  the  small  epithelial  plate  at  the  dorsal  end  of  the  lamina  ter- 
minalis. 

In  most  vertebrates  there  arises  out  of  that  part  of  the  forebrain  which 
lies  dorsally  and  laterally  from  the  lamina  terminalis  a  new  and  important 
structure,  the  Prosencephalon:  a  large  vesicle  located  anteriorly  and  dor- 
sally, which  is  soon  divided  into  right  and  left  hemispheres  by  a  longitudinal 


50  ANATOMY    OF   THE    CENTRAL    NERVOUS    SYSTEM. 

infolding  from  the  dorsal  surface.  The  hemispheres  are  not  developed  in 
the  sturgeon;  but,  even  if  they  were,  they  would  not  be  shown  in  Fig.  18, 
because  the  section  is  median. 

In  mammals,  the  hemispheres,  which  are  at  first  very  insignificant 
appearing  structures,  soon  grow  enormously,  bending  posteriorly  and  thus 
covering  gradually  most  of  the  other  vesicles.  Finally  they  rest  like  a 
mantle  over  the  Thalamencephalon,  the  Mesencephalon  (Corpora  Quadri- 
gemina),  and  the  Metencephalon  (Cerebellum  and  Pons). 

Notwithstanding  the  turning  back  of  the  cerebral  hemispheres,  the 


Fig.  20. — Median  longitudinal  section  through  the  brain  of  a  five-weeks' 
human  embryo.     (After  His.) 


cavities  of  the  various  brain-vesicles,  later  called  ventricles,  retain  their 
communication  with  each  other. 

Thus  from  the  primitive  forebrain- vesicle  two  structures  are  developed: 
Prosencephalon,  or  cerebrum  (Vorderhirn),  and,  from  that  part  of  the  primi- 
tive forebrain -vesicle  which  is  not  divided  into  hemispheres,  the  Thalamen- 
cephalon (Zwischenhirn). 

In  all  mammals  the  walls  of  the  hemispheres  begin  to  grow  thicker  at 
this  stage.  But  one  soon  discovers  that  that  process  is  carried  on  by  no 
means  equally.  Near  the  base  are  located  the  olfactory  lobes  as  thick-walled 
masses  and  posterior  to  them,  also  basal,  the  great  corpora  striata.  These 


DEVELOPMENT    OF    THE    BRAIN   AND    GANGLIA. 


51 


masses  are  separated  by  a  cleft  from  a  more  dorsal  segment,  the  Pallium,  or 
mantle,  whose  walls  thicken  relatively  late.  It  is  interesting  to  note  the 
primitive  relations  which  manifest  themselves  here.  In  all  vertebrates  the 
basal  ganglia — corpora  striata  and  olfactory  lobes — are  developed,  but  only 
among  the  higher  vertebrates  does  the  mantle  reach  a  noteworthy  develop- 
ment. In  Petromyzon  and  in  bony  fishes  the  mantle  remains  a  simple 
epithelial  wall  throughout  life.  But  the  Pallium  is  that  portion  of  the  brain 
which  later  bears  the  cortex  cerebri,  and  is,  therefore,  the  organ  on  whose 
development  all  higher  psychical  life  depends.  The  Pallium  of  the  stur- 
geon, for  example,  remains  through  life  as  thin  as  it  is  represented  in  the 
four  months'  embryo  (Fig.  18). 


Commiss.post. 


Vitrlijgtl. 


Hum* 


Fig.  21. — Longitudinal  section  of  head  of  a  four-and-a-half  day  chick.  The 
five  brain-vesicles  are  fairly  well  developed.  Vorderhirnhohle,  Cerebral  cavity. 
Zwischenhirnhohle,  Thalamencephalic  cavity,  or  third  ventricle.  MittleMrn- 
hohle,  Aquaeductus.  Hinterhirnhohle,  Cerebellar  cavity.  NachMrnhohle,  Cavity 
of  medulla.  The  last  two  together  form  the  fourth  ventricle.  Hypophysenanlage, 
Fundament  of  the  hypophysis.  Vierhiigle,  Corpora  Quadrigemina.  (After  von 
Mihalkovics.) 


The  hemispheres  are,  in  mammals,  most  highly  developed,  and  are  also 
here  best  studied.  Their  development  should  be,  therefore,  especially  de- 
scribed at  this  point;  while  those  parts  of  the  brain  which  He  posterior  to 
the  cerebrum  may  better  be  described  after  we  are  acquainted  with  the 
brains  of  lower  animals  where  the  thalamus,  and  midbrain,  and  even  the 
cerebellum  show  especial  structural  forms,  which  are  either  insignificant  or 
quite  lost  in  mammals.  The  roof  of  the  Thalamencephalon  remains  through 


52  ANATOMY    OF   THE    CENTRAL   NERVOUS    SYSTEM. 

life  for  nearly  its  whole  length  as  a  simple  epithelial  layer.  At  the  point 
of  juncture  with  the  Prosencephalon  the  epithelial  plate  is  displaced  down- 
ward by  the  encroachment  of  a  highly-vascular  growth  from  the  cranial 
cavity:  the  velum  chorioideum.  From  the  relation  of  the  hemispheres  to  the 
Thalamencephalon,  their  inner  border  must  be  continuous  with  the  velum. 
In  the  frontal  section  through  the  cerebrum,  shown  in  Fig.  22,  this  is  made 
apparent.  The  figure  also  shows  that  the  cerebral  cavity  is  divided  into 


Fjg.  22. — Frontal  section  through  the  head  of  a  human  embryo  of  two  and 
a  half  months,  showing  the  invagination  of  the  cerebral  cavity  and  the  fundament 
of  the  corpus  striatum. 


one  median  and  two  lateral  ventricles.  The  velum  chorioideum  sends  ex- 
pansions into  the  lateral  ventricles:  the  Plexus  chorioidei  laterales.  The 
place  where  the  walls  of  the  hemispheres  pass  into  a  simple  epithelial  layer 
(Fig.  22,  a)  is  called  the  margin  of  the  hemispheres.  This  margin  is  later 
marked  by  a  fasciculus  of  white  fibers  throughout  its  whole  length: 
Fornix. 

When  the  most  important  parts  of  the  cerebrum  have  once  become 


DEVELOPMENT    OF    THE    BRAIN   -AND   GANGLIA.  53 

well  defined,  it  has  the  form  shown  in  Fig.  23.  It  has  grown  out  pos- 
teriorly and  has  also  bent  ventrally.  Where,  within  the  cerebral  cavity,  the 
corpus  striatum  is  developing  the  outer  wall  is  less  expanded  than  in  the 
other  parts  of  the  cerebrum. 

In  that  place  a  relative  retardation  of  the  growth  of  the  cerebral  wall 
leaves  a  deep  fissure,  the  Fossa  Sylvii. 

A  frontal  lobe,  an  occipital  lobe,  and  a  parietal  lobe  may  now  be  easily 
distinguished  upon  the  hemispheres.  That  part  of  the  hemispheres  below 
the  Sylvian  fossa  is  called  the  temporal  lobe. 

The  hemispheres  are  still  hollow  within  and  the  ventricular  cavities 
conform  naturally  to  the  general  cerebral  form.  Those  parts  of  the  ven- 
tricle which  extend  into  the  frontal,  occipital,  and  temporal  lobes  have 
been  called  the  anterior,  posterior,  and  inferior  horns,  respectively.  At  this 
stage  of  development  the  median  wall  of  the  hemisphere  demands  our 


Fig.  23. — The  brain  of  a  human  foetus  of  the  fourth  month. 


especial  interest.  As  before  mentioned,  its  ventral  margin  passes  into  the 
epithelium  of  the  plexus  chorioideus.  This  is  the  case  also  when  the  wall 
bends  down  with  the  temporal  lobe.  From  the  base  of  the  lamina  terminalis 
to  the  apex  of  the  temporal  lobe,  the  sickle-shaped  fornix  locates  this 
margin.  In  the  anterior  part  of  the  brain  the  corpus  callosum  is  developed 
dorsal  to  the  fornix.  The  commissural  fibers  of  which  the  corpus  callosum 
is  composed  determine  a  surface  which  forms  an  acute  angle  with  the  fornix 
(see  Fig.  24). 

That  portion  remaining  between  corpus  callosum  and  fornix,  and  which 
consists  of  the  two  thin  laminae  of  the  primitive  hemispherical  division- 
wall  (primdre  scheidewand,  Fig.  22)  is  called  the  septum  pellucidum.  These 
are  important  structures,  which  should  be  carefully  studied  in  the  accom- 
panying figures. 

Note  carefully  the  anatomical  relations  shown  in  Fig.  22.    In  the  base 


54  ANATOMY    OF    THE    CENTRAL    NERVOUS    SYSTEM. 

of  the  cerebrum  is  a  thickening  of  the  wall,  which  projects  freely  into  the 
ventricle:  the  corpus  striatum.  From  the  corpus  striatum  as  from  the 
cerebral  cortex  nerve-fibers  arise. 

Many  fibers  which  have  their  origin  in  the  cerebrum  must  pass  through 
the  corpus  striatum  on  their  way  to  more  distant  parts  of  the  central  nervous 
system.  The  fibers  thus  passing  through  the  corpus  striatum  lie  in  two 
masses:  an  outer  and  an  inner  one.  The  outer  one  is  called  the  nucleus 
lentiformis  and  the  inner  one  the  nucleus  caudatus.  The  mass  of  fibers 
between  the  two  has  received  the  name  internal  capsule.  In  the  four  months' 
human  embryo  the  division  of  the  corpus  striatum  is  already  clear,  and  the 
nucleus  lentiformis  and  nucleus  caudatus  appear  as  independent  gray 
masses. 

The  corpus  striatum  lies  the  whole  length  of  the  cerebral  base.    Pos- 


Fig.  24. — Showing  median  aspect  of  a  hemisphere  whose  lateral  or  outer 
aspect  is  shown  in  Fig.  23.  Stelle  wo  Yorderhirn  u.  Zwischenhirn  Zusammen- 
stossen,  Place  where  cerebrum  and  Thalamencephalon  come  together.  For  further 
description,  see  text. 


teriorly  it  is,  indeed,  very  narrow  and  it  is  really  only  the  median  part 
which  is  always  demonstrable.  As  tail  of  the  caudate  nucleus,  it  is  always 
found  in  cross-sections  through  the  cerebrum.  The  lateral  part,  the  nucleus 
lentiformis,  is  much  shorter.  The  nucleus  caudatus  projects  freely  into  the 
ventricle.  The  same  is  true,  anteriorly,  of  the  nucleus  lentiformis.  In  later 
embryonic  life,  however,  the  narrow  cleft  between  it  and  the  cerebral  wall 
becomes  so  narrow  as  to  be  no  longer  demonstrable.  But  the  cerebral  wall 
may  always,  even  in  adults,  be  easily  separated  from  the  outer  wall  of  the 
nucleus  lentiformis,  without  the  severing  of  fibers. 

In  the  adult  brain  the  position  of  the  former  cleft  may  become  of  great 
importance.  At  that  place,  for  example,  cerebral  hemorrhages  take  place 
with  especial  ease,  and  the  blood,  even  when  it  is  small  in  quantity,  fills  the 
space  between  the  cerebral  wall  and  the  outer  side  of  the  nucleus  lentiformis. 


DEVELOPMENT  OF  THE  BRAIN  AND  GANGLIA.  55 

The  glimpse  which  has  been  presented  of  the  developing  brain  has 
possibly  already  called  forth  the  question:  How  does  the  brain  grow?  And 
the  comparison  with  the  richly  convoluted  brain  of  the  adult  may  have 
suggested  also  the  question:  At  about  what  time  has  the  brain  reached  the 
form  and  size  which  it  retains  through  the  major  part  of  life  or  until  that 
time  when  advancing  age  induces  senile  decadence? 

If  the  brain  is  the  organ  upon  the  faultless  performance  of  whose 
function  the  normal  psychical  processes  depend,  it  is  worth  our  while  to 
know  how  long  new  tissue-elements  may  be  formed  and  upon  the  in- 
crease of  what  part  the  growth  of  the  whole  depends.  Investigations  which 
might  answer  these  important  questions  have  made  little  advance.  There 
is  a  complete  lack  of  investigations  on  the  multiplication  of  ganglion- 
cells  in  different  parts  of  the  brain  in  the  post-embryonic  period.  Up 
to  the  present  time  karyokinesis  of  nuclei  of  central  cells  has  been  very 
infrequently  found;  so  that  it  might  appear  as  if  the  brain,  which  has 
approximately  reached  the  form  and  weight  of  the  adult  organ  at  about 
the  seventh  year,  had,  by  that  time,  established  all  of  its  ganglion-cells. 
Schiller's  proof,  that  the  slender  oculomotorius  of  the  newborn  cat  contains 
scarcely  fewer  fibers  than  the  thick  nerve  of  the  adult,  favors  the  theory  of 
an  early  termination  of  cell-formation.  There  are,  however,  opposing  state- 
ments. Thus,  Kayser  found  in  the  cervical  enlargement  of  the  spinal  cord 
of  the  newborn  only  about  half  as  many  ganglion-cells  as  in  the  same 
region  of  a  15-year-old  b9y,  while  the  number  found  in  the  latter  case  was 
little  different  from  that  found  in  an  adult  man.  Also  enumerations  which 
Birge  and  others  have  made  on  the  spinal  cord  of  the  frog  determined 
positively  that  in  these  animals  the  ganglion-cells  continue  to  increase  for  a 
long  time  in  adult  life. 

Probably  the  principal  post-embryonal  increase  of  nerve-tissue  in  man 
occurs  in  the  growth  of  nerve-fibers  and  collaterals  from  ganglion-cells 
already  present,  and  especially  of  the  formation  of  medullary  substance 
which  continues  throughout  life.  Donaldson,  to  whom  we  are  indebted  for 
an  excellent  work  on  "The  Growth  of  the  Brain,"  came  to  the  same 
conclusion. 

The  human  cerebrum  having  been  an  important  object  of  your  previous 
study,  it  has  seemed  profitable  to  describe  its  development  somewhat  in 
detail.  But  since  we  are  not  here  concerned  with  the  human  brain  alone, 
let  us  study  in  the  brain  of  another  vertebrate  those  first  developmental 
processes  which  are  common  to  all  vertebrates.  For  this  the  brain  of  a 
reptile — the  lizard — has  been  chosen.  In  this  (see  Fig.  25)  one  may  readily 
recognize  the  typical  parts  of  the  vertebrate  brain,  because  even  in  adult 
reptiles  the  relations  are  much  simpler  than  in  mammals. 

The  middle  of  the  figure  is  occupied  by  the  cavity  of  Thalamen- 


56 


ANATOMY   OF   THE    CENTRAL   NERVOUS    SYSTEM. 


cephalon.  Its  roof  is  almost  exclusive!}7  formed  of  epithelial  plates  whose 
numerous  projections  will  claim  our  attention  later.  Even  ventrally  the 
wall,  which  is  evaginated  to  form  the  sack-like  recessus  infundibular  is,  is 
only  a  thin  one.  The  hypophysis  lies  close  beside  it.  The  lateral  walls  con- 
taining the  optic  thalami  are  not  figured.  The  dorsal  wall  of  the  Thala- 
mencephalon  is  directly  continuous  with  the  cerebral  mantle,  the  Pallium, 
which  is  the  dorsal  wall  of  the  Prosencephalon.  The  floor  of  the  latter  is 
occupied  by  the  corpus  striatum  and  the  olfactory  apparatus.  Posteriorly 
the  Thalamencephalon  merges  into  the  Mesencephalon,  whose  dorsal  seg- 
ment is  called  the  corpus  opticum,  .because  here  is  the  deep  origin  of  the  optic 
nerves. 

The  ventral  segment  of  the  midbrain,  designated  as  Tegmental  promi- 
nence (Haubenwulsf)  and  Basis  mesencephali,  contains  almost  exclusively 


Fig.  25. — Eeptilian  brain.     (A  diagrammatic  sagittal  section.) 


nerve-tracts,  with,  also,  a  few  small  nuclei.  Turning  at  a  sharp  angle,  the 
corpus  opticum  becomes  continuous  with  the  cerebellum.  In  this  angle 
there  are,  in  all  vertebrates,  two  great  nerve-decussations,  the  anterior  one  of 
which  belongs  to  the  nervus  trochlearis.  The  cerebellum  covers  a  part  of 
the  medulla  even  in  the  reptile.  The  greater  part,  however,  is  exposed  and 
is  covered  by  a  thin  choroid  plexus:  the  Plexus  ventriculi  quarti.  Then 
the  cavity  of  the  central  system  becomes  narrower  and  narrower  until  it  be- 
comes a  narrow  canal  which  traverses  the  whole  length  of  the  spinal  cord. 
Something  has  been  said  of  the  development  of  the  peripheral  nerves 
in  the  previous  chapters.  If  the  central  nervous  system  has  progressed  so 
far  in  its  development  that  the  principal  parts  are  clearly  distinguished  one 
from  another,  then  from  the  Thalamencephalon  to  the  end  of  the  spinal 
cord  the  central  cavity  (ventricle,  or  central  canal)  is  inclosed  with  gray 
tissue:  masses  rich  in  ganglion-cells.  Posterior  to  the  midbrain  the  periph- 


DEVELOPMENT  OF  THE  BRAIN  AND  GANGLIA.  57 

oral  nerves  arise  from  these  ganglion-cells.  The  motor  nerves  arise  from 
cell-groups  in  the  gray  matter,  and  with  few  exceptions  leave  the  spinal  cord 
by  the  ventral  side.  Most  of  the  sensory  nerves  arise  from  ganglia  which 
lie  close  beside  the  central  organ. 

From  the  ganglion  every  sensory  nerve  sends  a  number  of  root-fibers 
dorsally  into  the  central  nervous  system.  Most  of  the  sensory  root-fibers 
pass  into  the  gray  substance  not  far  from  the  respective  ganglia,  but  some 
of  them  run  some  distance,  forward  or  backward,  in  the  superficial  layers 
before  they  reach  their  termination  in  the  gray.  These  are  designated  as 
ascending  and  descending  roots.  The  origin  and  arrangement  of  the  ganglia 
afford  much  instruction  and  interest. 

The  earliest  embryonic  changes  show  that  in  these  peripheral  structures 
we  have  to  deal  with  true  derivatives  of  the  central  nervous  system, — with 
parts  which  separated  from  it  quite  early.  The  ganglia  arise  from  the  mar- 
gins (Randstreifen)  of  the  medullary  plate.  When  this  plate  rises  on  eacli 
side  to  form  the  medullary  ridges  which  finally  fuse  along  their  marginal 
lips  to  form  the  medullary  canal,  leaving  on  each  side  a  free  edge,  these 
margins  come  together  and  form  an  unpaired  cell-rod,  which,  at  first 
wedge-shaped,  appears  to  sink  more  or  less  into  the  dorsal  seam  of  the 
spinal  cord.  In  consequence  of  an  increase  and  a  displacement  of  its  cells  it 
soon  leaves  this  position,  leaves  the  roof  of  the  medullary  tube  completely, 
and  is  divided  by  splitting  longitudinally  into  a  left  and  right  cord. 
Through  segmental  thickening  the  paired  fundaments  are  divided  into  sepa- 
rate ganglia,  which  move  more  and  more  laterally  along  the  medullary  tube. 
When  the  segmentation  is  complete  then  the  primary  ganglia,  so  far  as 
they  are  derived  from  elements  of  the  central  system,  are  complete. 

While  the  spinal  ganglia,  from  their  above-described  derivation,  re- 
main really  a  part  of  the  central  system,  the  ganglia  of  the  cranial  segment 
come  into  renewed  contact  with  the  ectoderm,  or,  more  correctly,  with  the 
embryonic  epidermis  for  a  certain  period  of  their  development,  and  together 
with  this  form  the  fundaments  of  the  primitive  sense-organs.  Every  cranial 
nerve  acquires  two  such  contacts,  or  forms  fundaments  of  two  sense-organs, 
at  two  typical  locations.  These  locations  for  the  several  cranial  nerves 
occur  in  two  longitudinal  series:  one  more  dorsally  located,  the  lateral, 
or  Kupffer' s,  fundament,  and  one  more  ventrally  located,  the  epibranchial, 
or  Froriep's,  fundament.  All  of  the  Kupffer  fundaments  occur  in  a  longi- 
tudinal line  which  begins  anteriorly  in  the  olfactory  pit,  passes  through  the 
oral  pit,  and  in  lower  vertebrates  is  continued  along  the  body  as  the  lateral 
line.  All  of  the  Froriep  fundaments  lie  in  a  longitudinal  line  which  begins 
anteriorly  in  the  lens-pit  (Linsengrube)  and  thence  runs  along  the  dorsal 
ends  of  all  the  branchial  slits.  Of  the  Kupffer  fundaments  two  persist  and 
develop  into  permanent  sense-organs:  the  nasal  pit  and  the  auditory  pit. 


58  ANATOMY    OF   THE    CENTRAL    NERVOUS    SYSTEM. 

The  Froriep  fundaments,  on  the  other  hand,  have  an  exclusively  embryonic 
existence,  and  were,  therefore,  regarded  by  their  discoverers  as  ontogenet- 
ically  persistent  rudiments  of  lost  ancestral  sense-organs;  and  were  called 
branchial  cleft  organs  (Kiemenspaltenorgane).  Definite  traces  of  this  embry- 
onic connection  with  the  epidermis  are  manifest  in  the  adult  in  the  Acustico- 
facialis,  the  Glosso-pharyngeus,  and  Vagus;  the  Kupffer  series  corresponds 
to  the  Ggl.  acusticum,  Ggl.  jugulare  of  the  IX  and  the  Ggl.  jugulare  of  the 
X;  from  the  Froriep  series  arise  the  Ggl.  geniculatum  (VII),  Ggl.  petrosum 
(IX),  and  the  pneumogastric  ganglion  (X). 


i/ntestinu/n. 


Fig.  26a. — Cross-section  through  the  posterior  part  of  the  head  of  a  shark 
embryo,  of  twelve  millimeters'  length.  The  section  passes  through  the  fourth 
visceral  cleft  (4)  and  through  the  vagus  ganglion  with  its  two  epidermal  con- 
tacts: the  Kupffer  fundament  (Kupffer  Anl.)  and  the  Froriep  fundament,  re- 
spectively,— the  lateral  and  the  epibranchial  fundaments,  rt,  fl,  Arteries,  v, 
Jugular  vein.  (After  Froriep.) 


The  olfactory  nerve  occupies  an  exceptional  position.  At  one  time 
its  primitive  ganglion  seemed  to  be  quite  absent.  The  olfactory  ganglion  of 
His  arises  independent  of  the  nasal  pit — the  Kupffer  fundament — as  a 
purely  lateral  ganglion,  migrates  away  from  the  nasal  pit,  approaches  the 
brain,  and  fuses  completely  with  the  olfactory  bulb.  The  nasal  pit  behaves 
also  in  a  special  way,  in  so  far  as  it  is  the  only  one  of  the  persistent  funda- 
ments which  retains  the  character  of  the  primitive  sense-organs.  Its  cells 
remain  in  situ  as  peripheral  nerve-cells  which  send  their  neuraxons  into  the 
olfactory  bulb.  In  the  case  of  other  sense-organs — e.g.,  the  auditory  pit — a 
separation  takes  place:  the  original  peripheral  nerve-cells  migrate  inward 


DEVELOPMENT  OF  THE  BKAIN  AND  GAXGLIA.  59 

and  become  bipolar  or  pseudo-unipolar  ganglion-cells,  while  the  cells  of  the 
fundament  which  remain  superficial  become  differentiated  into  "secondary 
.sense-cells"  of  Eetzius  (Froriep). 

While  the  relations  in  the  trunk  are  quite  simple,— -since  here  a  series 
of  spinal  ganglia  lie  beside  the  spinal  cord, — those  in  the  head  will  be 
found  to  present  a  much  more  complicated  arrangement.  It  is  exceedingly 
important  here  to  obtain  a  clearer  idea  as  to  the  number  of  fundaments 
or  primitive  elements  which  enter  into  these  structures,  because  in  all 
.adult  vertebrates  of  higher  rank  the  relations  presented  by  the  cranial  nerves 
are  so  complicated  that  the  opinion  has  long  been  held  that  these  nerves  are 
not  completely  homologous  to  spinal  nerves,  but  that  all  or  nearly  all  of 
them  are  compounded  from  several  elements  into  an  apparently  unified 
structure.  Twelve  pairs  of  cranial  nerves  are  usually  differentiated  in  mam- 
mals; even  in  birds  the  same  thing  may  be  true;  but  in  amphibians  and  espe- 
cially in  fishes  such  an  enumeration  is  quite  arbitrary.  In  these  lower  verte- 
brates not  only  do  the  nerve-trunks  receive  other  branches  than  those  typical 
of  the  higher  animals,  but  the  sources  of  the  roots  are  so  manifold  that  it 
is  not  always  possible  to  determine  whether  a  particular  root  belongs  to  one 
nerve  or  another.  For  example,  the  Facialis  consists  essentially  of  motor 
fibers  in  the  higher  vertebrates,  but  in  the  aquatic  lower  vertebrates  it  re- 
ceives a  large  reinforcement  of  sensory  fibers  which  belong  to  the  system  of 
cutaneous  sense-organs.  Thus  there  exists  no  little  confusion  in  differen- 
tiation of  the  Facialis  and  Trigeminus. 

The  cephalic  end  of  the  skeleton  is  phylogenetically  compounded  from 
;a  number  of  segments  which  have  not  yet  with  certainty  been  determined. 
It  is  probable  that  the  number  of  ganglia  and  the  nature  of  the  nerve-roots 
may  serve  as  guides  in  this  problem.  It  thus  becomes  an  important  task  to 
determine:  (1)  how  many  primitive  pairs  of  cranial  nerves  there  are,  and  (2) 
how  these  have  been  transformed  and  combined  to  form  the  cranial  nerves 
which  we  find  in  the  higher  vertebrates.  Incident  to  the  transformation 
•certain  previously  large  and  important  nerves  become  superfluous  and  dis- 
appear, others  change  the  direction  of  their  course,  and  still  others  pass  to 
organs  which,  during  the  racial  or  individual  development,  have  had  a 
function  quite  different  from  that  which  they  have  in  the  mature  condition. 
For  example,  from  the  embryonic  branchial  fundaments  important  parts  of 
the  skull  and  of  the  middle  ear  develop;  the  branchial  nerves  are  modified 
along  with  the  other  structures,  and  appear  later  in  a  role  wholly  different 
from  that  which  they  originally  played  (e.g.,  1ST.  petrosus  superfic.).  In  fishes 
and  aquatic  amphibians  the  skin  of  the  head  is  covered  with  a  system  of 
sensory  end-organs  which  possibly  serve  for  the  perception  of  the  changes 
of  pressure  in  the  surrounding  medium.  The  sensory  branches  of  the 
Facialis  which  in  Amphibia  innervate  these  organs  are,  in  the  metamor- 


60 


AXATOMY    OF    THE    CENTRAL   NERVOUS    SYSTEM. 


phosis  to  terrestrial  amphibia,  either  lost  or  changed  to  quite  insignificant 
twigs. 

In  the  light  of  these  facts  it  becomes  evident  that  the  formerly  practical 
method  of  a  simple  morphological  description  of  that  which  exists  in  the 
adult  animal,  and  above  all  the  simple  transferring  of  mammalian  relations 


N.l.p.         G.V.  Of.      G.ff.f 


R.r.V. 


266. — Cranial  ganglia  and  nerves  of  a  four-millimeter  Ammocoetes. 
(After  Kupffer.) 


R.y. 
R.IV.         G.V.     '• 


Ro.t. 


Ng.  G.G. 


Fig.  26c. — Cranial  ganglia  and  nerves  of  a  twelve-centimeter  Ammoccetes. 
(After  Kupffer.) 

Explanation  of  the  figures:  G.o.,  Ganglion  ophthalmicum.  R.o.t.,  Radix 
ophthal.  N.  trigem.  N.t.,  Mervus  trigeminus.  R.N.t.,  Radices  X.  trigem.  G.m.m., 
Ggl.  maxillo-mandibulare.  G.N.f.,  Ggl.  N.  facialis.  R.N.f.,  Radix  N.  facialis. 
Ot.,  Otocyst.  G.G.,  Ggl.  N.  glosso-pharyngei.  G.V.,  Ggl.  Vagi.  N.ff.,  N".  glosso- 
pharyngeus.  N.l.p.,  N.  lateralis  prof.  R.I.V.,  Ramus  lat.  Vagi.  R.T.,  Radices  N. 
Vagi.  R.N.T. ,  Rami  N.  Vagi.  1,  6,  8,  10,  Epibranchial  ganglia  of  these  numbers,, 
respectively. 


DEVELOPMENT    OF   THE    BRAIN   AND    GANGLIA.  61 

to  the  lower  vertebrates,  can  lead  to  no  satisfactory  results.  The  task  of 
sufficiently  describing  the  cranial  nerves  is  to  be  accomplished  in  no  other 
way  than  the  following:  (1)  in  gradually  becoming  acquainted  with  all  of 
the  separate  nerves  that  correspond  to  a  single  segment  of  the  head,  and  (2) 
in  determining  how  these  have  been  combined  into  larger  trunks. 

So  far  as  we  know  at  present,  the  simplest  relations  exist  in  the  embryos 
of  Cyclostomii.  It  is  especially  to  Kupffer  that  we  are  indebted  for  the 
beginning  of  a  somewhat  clearer  vision  here.  (See  Figs.  26&  and  26c.) 

Note  in  the  Ammoccetes  of  only  four  millimeters  that  the  chain  of 
epibranchial  ganglia  is  connected  dorsally  with  the  five  much  larger  dorso- 
lateral  ganglia.  The  most  anterior  one  of  the  latter  is  the  Ggl.  ophthal- 
micum.  From  this  most  of  the  fibers  which  constitute  the  ophthalmic 
branch  of  the  Trigeminus  later  develop.  Posterior  to  this,  and  connected 
with  the  central  system  through  two  roots,  lies  the  Ggl.  maxillo-mandibulare. 
It  will  later  be  fused  with  the  Ggl.  ophthalmicum  to  form  the  Ganglion  Gas- 
seri  and  will  give  off  the  second  and  third  branches  of  the  Trigeminus.  But 
in  the  meantime,  fibers  and  ganglion-cells  from  the  anterior  epibranchial 
ganglia  have  become  associated  with  the  elements  already  enumerated.  So 
the  N.  trigeminus  is  to  be  looked  upon  as  already  a  most  complicated  struct- 
ure, containing  elements  of  most  varied  origin.  Anterior  to  the  otocyst 
lies  the  great  ganglion  of  the  Facialis,  connected  with  the  sixth  and  seventh 
epibranchial  ganglia.  When  the  animal  becomes  larger  one  recognizes  that 
this  ganglion  is  only  an  appendage  of  the  great  composite  root  of  the 
Facialis;  that  in  the  composition  of  this  nerve  not  only  do  fibers  from  the 
ganglion  in  question  participate,  but  also  numerous  structures  which  arise 
from  the  now  gradually  disappearing  epibranchial  ganglia.  Just  posterior 
to  the  ganglion  of  the  Facialis  the  previously  continuous  trunk  of  the  epi- 
branchial ganglia  comes  to  an  end  (see  Fig.  26c  and  compare  Fig.  26&). 
Parts  of  this  trunk  are  received  anteriorly  into  a  Eamus  'buccalis,  and  pos- 
teriorly into  peripheral  facial  branches. 

Here  is  an  example  of  that  which  the  author  stated  above  regarding 
the  value  or  significance  of  single  nerves.  The  apparently  single  facial 
nerve  contains  elements  of  the  most  manifold  origin  and  significance. 

Posterior  to  the  otocyst  lie  the  Ggl.  Glosso-pharyngei  and  the  Ggl.  Vagi; 
both  intimately  connected  with  the  corresponding  epibranchial  ganglia. 
Later,  when  the  epibranchial  chain  is  broken,  it  remains  intact  posterior 
to  the  ganglion  of  the  Vagus,  where  it  appears  like  a  nerve-trunk  passing  off 
from  that  ganglion  and  containing  ganglionic  nodes.  It  is  the  1ST.  pneumo- 
gastricus,  the  Vagus,  and  it  innervates  the  gills,  heart,  and  other  viscera. 


CHAPTEE    V. 

THE   STEUCTUEE   OF  THE   SPIXAL   COED. 

IK  the  introductory  chapters  the  fundamental  elements  of  which  the 
nervous  system  is  composed  were  presented;  also  their  arrangement  in 
larger  and  smaller  complexes,  and  the  development  of  these  and  the  princi- 
pal divisions  of  the  central  system.  In  the  following  chapters  will  be  pre- 
sented the  most  important  facts  known  regarding  the  structure  of  these 
principal  divisions,  beginning  with  the  description  of  the  best-known  nerv- 
ous systems:  the  mammalian  and  human. 

First  to  be  considered  is  the  spinal  cord,  the  lowest  central  nervous 
system,  the  one  which  is  always  present,  and  which  forms  the  first  place  of 
reception  and  place  of  origin  of  nerves.  On  either  side  of  it  lie  the  spinal 
ganglia  from  whose  cells  the  sensory  nerves  take  their  origin.  They  have 
been  found  in  vertebrates  of  all  classes.  The  ganglia  are  constructed  of 
cells  whose  large  bodies  send  out,  in  fishes,  an  axis-cylinder  in  each  direction, 
the  efferent  one  being  the  neuraxon,  while  the  afferent  one  represents  a 
modified  dendrite  (see  Fig.  16,  in  Chapter  II).  The  same  is  true  in  the 
embryos  of  other  vertebrates;  but  in  the  latter  the  processes  come  to  lie  so 
close  together  that  the  first  part  of  their  course  is  represented  by  a  single 
stalk,  only  dividing  a  little  way  beyond  the  point  of  origin.  Fig.  27  shows 
several  such  cell-types  from  spinal  ganglia.  Wherever  it  has  been  investi- 
gated it  has  been  found  that  one  of  the  processes  ran  to  the  periphery  as 
sensory  nerve  while  the  other  passed  to  the  central  organ.  All  of  these 
central  processes  taken  together  are  called  the  dorsal  root  of  the  ganglion. 
The  number  of  dorsal  roots  is  very  different  in  different  animals;  even 
among  individuals  of  the  same  species  there  may  be  small  variations.  That 
depends  upon  the  length  of  the  animal  and  the  number  of  the  metameres 
which  reach  structural  maturity.  Ranged  serially  along  the  sides  of  the 
spinal  cord  these  sensory  roots  enter  the  cord  from  the  dorsal  side.  After 
their  entrance  they  divide  into  ascending  and  descending  branches,  and 
also  give  off  numerous  collateral  branches,  which  send  twigs  into  the  gray 
matter.  This  ascent  and  descent  occurs  in  the  dorsal  segment  of  the  spinal 
cord,  and  where  many  such  nerves  are  present  the  whole  bundle  of  longi- 
tudinally ranged  nerves  is  called  the  posterior  tracts. 

Any  section  of  the  spinal  cord  shows  that  that  organ  is  traversed 
centrally  and  longitudinally  by  a  canal — canalis  centralis — surrounded  by 

(62) 


STRUCTURE    OF    THE    SPINAL    CORD. 


63 


epithelium,  and  that  around  this  canal  lies  a  very  finely  organized  tissue, 
the  gray  substance.  This  is,  in  turn,  surrounded  by  nerve-fibers,  most  of 
which  run  longitudinally.  These  longitudinal  nerve-fibers  represent  the 
tracts.  • 

The  posterior  root-fibers  (dorsal  roots)  enter  the  gray  substance  after 
a  longer  or  shorter  course,  usually  in  the  posterior  tracts,  though  in  fishes 
in  laterally  located  tracts  as  well.  After  entering  the  gray  substance  the 
fibers  divide  into  fine  terminal  ramifications,  which  join  a  close  net-work 
of  fibrillae,  which  fills  the  whole  posterior  segment  of  the  gray  matter. 
They  probably  come  into  contact  there  with  the  processes  of  smaller  cells. 


Fig.  27. — Several  forms  of  spinal  ganglion-cells,  showing  the  cell-bodies,  the 
afferent  sensory  nerves,  and  the  dorsal  roots  (Hintere  Wurzel). 


The  gray  matter  has  been  divided  into  posterior  and  anterior  horns.  A 
better  expression  would  be:  dorsal  and  ventral  columns,  because  the  projec- 
tions are  really  columns  which  extend  longitudinally  throughout  the  whole 
length  of  the  cord.  The  dorsal  columns  are  formed  from  the  fiber  mesh-work 
of  the  posterior  roots.  The  ventral  columns  are  formed  from  the  collec- 
tion of  ganglion-cells  which  give  rise  to  the  anterior  roots. 

The  development  of  the  dorsal  and  ventral  columns  depends  naturally 
upon  the  number  of  nerve-fibers  which  are  connected  with  them.  The  fishes 
furnish  a  good  example  of  this.  In  this  class  of  vertebrates  a  large  part  of 
the  body-surface  is  supplied  with  sensory  fibers,  not  from  the  spinal  nerves, 


64  ANATOMY   OF   THE    CENTRAL   NEEVOUS    SYSTEM. 

but  from  a  branch  of  the  Vagus.  The  spinal  sensory  nerves  are,  therefore, 
relatively  small,  and  in  consequence,  also,  the  dorsal  column  of  gray  matter, 
as  shown  in  Fig.  29. 

But  if,  as  in  the  case  of  Trigla  (Fig.  29,  B),  many  sensory  nerves  enter 
the  spinal  cord  at  any  particular  place,  the  dorsal  column  is  much  increased 
at  that  level.  Fig.  29,  A,  shows  a  section  of  the  spinal  cord  of  the  white- 
fish  (Leuciscus  rutilus).  Note  here  the  small  dorsal  columns  which  receive 


Fig.  28. — The  diagram  of  the  spinal  cord  as  seen  from  behind.  Showing  the 
dorsal  and  ventral  columns  of  the  gray  matter  and  the  dorsal  and  ventral  nerve- 
roots,  illustrating  also  what  was  said  about  the  posterior  tracts. 


relatively  small  roots.     Note,  also,  that  between  the  dorsal  columns  the 
posterior  tracts  contain  only  a  few  fibers. 

The  ventral  columns  from  which  the  motor  nerves  arise  are  relatively 
small  in  Trigla  in  the  cervical  region,  in  the  white-fish  they  are  very  much 
more  strongly  developed,  but  in  the  spinal  cord  of  the  electric  eel  (Gymno- 
tus,  Fig.  29,  (7)  they  reach  a  very  unusual  development.  In  the  last  case  the 


STRUCTURE    OF    THE    SPIXAL    CORD. 


65 


I£igs.  29,  30,  and  31.— Showing  the  different  degrees  of  development  of  the 
gray  matter.  A,  Spinal  cord  of  Leuciscus;  B,  of  Trigla-  C,  of  Gymnotus;  the 
last  from  a  preparation  by  von  Fritsch. 


66  ANATOMY    OF    THE    CEXTBAL    XEKYOUS    SYSTEM. 

column  in  question  contains,  besides  the  small  ganglion-cells  which  produce 
the  motor  nerves, — by  chance  not  shown  in  the  figure, — a  mass  of  immense 
spherical  ganglion-cells:  the  Nucleus  nervorum  electricorum.  These  cells 
certainly  correspond  to  a  group  of  motor  cells  in  other  animals;  but,  as  you 
know,  the  electric  organ  of  Gymnotus  is  shown  by  location  and  structure  to 
be  derived  from  muscular  tissue. 

After  their  entrance  into  the  spinal  cord  mo'st  of  the  posterior  root- 
fibers  soon  enter  the  gray  matter;  in  part,  however,  they  reach  the  gray 
matter  only  after  a  longer  or  shorter  course  in  the  posterior  tracts.  It  has 
been  found  that  a  small  number  of  the  root-fibers  actually  pass  through  the 
gray  matter,  crossing  over  to  the  dorsal  column  of  the  other  side  to  end 
immediately,  or  to  end  only  after  passing  along  the  posterior  tract  of  that 
side  for  a  certain  distance.  These  crossed  sensory  nerves  pass  from  one  side 
to  the  other  in  the  Commissura  dorsalis  medulla  spinalis.  They  are  very 
unequally  developed  in  different  animals,  even  in  animals  of  related  species. 
Besides  that,  the  commissura  dorsalis  is  unequally  developed  at  different 
levels  of  the  cord.  The  number  of  fibers  in  it  depends  upon  the  size  of  the 
posterior  roots,  and  from  the  proximity  of  this  to  the  point  of  section. 

A  certain  portion  of  the  posterior  roots  is  not  at  once  lost  in  the  net- 
work of  the  gray  matter,  but  proceeds  farther  ventrally  to  the  region  of  the 
ventral  column.  This  will  be  discussed  later. 

Finally  it  must  be  mentioned  that  in  mammals  a  part  of  the  sensory 
tract  comes  into  connection  with  cells  which  stand  in  direct  connection  with 
the  cerebellum  through  their  axis-cylinders.  These  cells  arranged  in  long 
columns — the  column  of  Stilling-Clarke — have  only  been  demonstrated  in 
mammals.  Their  presence  in  fishes,  reptiles,  and  birds  is,  however,  at  least 
probable,  though  their  certain  identification  has  not  yet  been  successful. 

Eemember  that  the  dorsal  columns  or  posterior  horns  owe  their  exist  - 
ence  to  the  entering  roots,  and  that  the  posterior  tracts  are  little  more  than 
the  continuation  of  root-fibers.  The  same  thing  is  true  for  a  part  of  the 
lateral  columns,  varying  with  different  orders  of  animals. 

Such  are  the  characteristics  of  the  apparatus  through  which  the  im- 
pressions of  the  outer  world  are  conducted  to  the  central  system.  Before 
tracing  the  course  of  the  afferent  impulses  within  the  central  system,  the 
origin  of  the  motor  nerves  will  be  described.  That  may  be  readily  done, 
since  the  essential  facts  have  already  been  presented.  Eemember  that  in  the 
ventral  column  (anterior  horn)  of  the  gray  matter,  lie  long  columns  of 
ganglion-cells  whose  neuraxons  for  the  greater  part  emerge  from  the  an- 
terior roots  of  the  same  side,  while  the  smaller  remaining  parts  cross  over 
and  emerge  from  the  opposite  root.  As  motor  nerves,  they  proceed  on 
their  course.  At  quite  regular  intervals  the  ventral  columns  form  ventrally 
projecting  prominences  of  the  spinal  gray  matter:  the  anterior  horns.  They 


STETJCTURE    OF    THE    SPIXAL    COED. 


67 


also  undergo  an  increase  in  size  at  places  where  many  root-fibers  leave  the 
cord.  Thus,  in  animals  with  legs  there  may  be  observed  an  enlargement  of 
the  spinal  cord  for  both  anterior  and  posterior  extremities,  the  Intu- 
mescentia  cervicalis  and  lumbalis,  respectively.  The  difference  in  this 
respect  between  lizards  and  the  snake-like  "blind  worms"  is  clearly  visible. 
The  enlargements  are  especially  noticeable  in  a  section  of  the  spinal  cord  of 
the  turtle,  because  these  armored  animals  have  very  large  nerves  to  supply 
the  extremities,  while  the  thoracic  nerves  are  very  small. 

The  columns  of  large  ganglion-cells  contain  the  centers  of  innervation 


Fig.  32. — Projection  upon  a  plane  of  the  enumerated  ganglion-cells  of  a 
frog's  spinal  cord.  The  figures  at  the  right  indicate  the  number  of  the  corre- 
sponding spinal  nerve.  Note  the  enormous  increase  of  the  number  of  cells  for 
arms  and  legs.  (After  Birge.) 


for  the  individual  muscles.  These  are  arranged  in  groups.  For  the  mam- 
malian spinal  cord  the  significance  of  a  few  of  these  groups  is  already 
known.  It  is  known,  for  example,  that  the  ganglion-cells  which  lie  nearest 
the  median  line  innervate  the  muscles  of  the  back;  and  that  a  certain 
group  of  laterally  located  cells  in  the  cervical  cord  provides  innervation  for 
the  musculature  of  the  thumb.  This  was  found  out  by  a  careful  study  of 


68 


ANATOMY    OF   THE    CENTRAL   NERVOUS    SYSTEM. 


the  spinal  cord  of  such  animals  as  had  suffered — through  disease  or  experi- 
ment— paralysis  of  a  particular  group  of  muscles,  comparing  the  microscopic 
appearances  with  those  of  the  normal  individual.  How  far  such  observa- 
tions have  been  made  in  the  human  subject  will  be  discussed  later. 

The  cell-groups  in  the  lower  vertebrates  appear  so  similar  to  those  in 
the  well-studied  mammals  that  one  is  justified  in  assuming  that  there  are' 
also  in  the  lower  vertebrates  definitely  circumscribed  centers. 

The  anterior  gray  horns  do  not,  moreover,  send  all  of  their  fibers 
through  the  anterior  roots.  It  has  been  demonstrated  for  representatives 
of  most  classes  of  vertebrates  that  a  very  large  bundle  of  fibres  passes  dorsally 
and  leaves  the  cord  by  the  posterior  roots  (see  Fig.  33). 

Since  motor  fibers  reach  the  sympathetic  nerve  through  the  posterior 


Fig.  33. — Section  through  spinal  cord  of  a  chick,  showing  motor  fibers  to  the 
dorsal  root  (Fibr.  mot.  ad  rad.  dors.).     (After  Retzius.) 


root-fibers  which  innervate  the  musculature  of  the  viscera,  it  is  probable 
that  in  the  above-mentioned  fibers  from  the  anterior  horn  we  see  the  motor 
nerves  of  the  viscera. 

The  two  ventral  cell-columns,  belonging  essentially  to  the  motor  sys- 
tem, and  the  two  dorsal  enlargements  of  the  gray  matter  which  receive  the 
sensory  roots  produce  upon  a  cross-section  of  the  spinal  cord  of  most  verte- 
brates a  gray  figure  similar  to  an  H. 

The  central  gray  matter,  in  addition  to  the  several  elements  already 
enumerated,  contains  such  innumerable  dendrites  and  collaterals  of  neu- 
raxons  from  the  root-cells  that  it  presents  a  perfect  labyrinth  of  meshes, 
into  which  enter  the  large  tracts  from  the  posterior  roots,  and  these,  pass- 
ing through,  ramify  about  the  cells  of  the  anterior  horn.  These  sensory 


STEUCTUEE    OF    THE    SPINAL    COED. 


G9 


elements,  which  lie  so  close  to  the  origin  of  the  motor  fibers,  would  be  well 
adapted  to  bring  about  directly  many  short  reflexes  (see  Fig.  34). 

Not  all  of  the  cells  in  the  spinal  cord  nor  all  of  the  fibers  stand  in 
direct  relation  to  nerve-roots.  There  are  very  many  cells  which  send  their 
neurite,  or  axis-cylinder,  out  of  the  gray  matter,  either  on  the  same  or 
opposite  side.  Usually  the  neurite  divides  then  into  an  ascending  and  a 
descending  branch.  Then,  after  a  longer  or  shorter  course,  again,  bending 


Fig.  34. — From  the  spinal  cord  of  a  newborn  mouse.     (After  Lenhossek.) 


back  into  the  gray  matter,  both  branches  end.  On  the  way  the  main 
branches  have  sent  numerous  collaterals  into  the  gray.  Such  cells  are 
adapted  to  connect  among  themselves  different  levels  of  the  spinal  cord. 
Such  neurons  are  called  cellulce  commissurales.  Many  neurites  from  such 
commissural  cells  cross  over  ventrally  to  the  opposite  side,  forming  a  decus- 
sation  quite  ventral  to  the  gray:  the  decussatio  ventralis  of  the  spinal  cord 
(Fig.  33,  Dec.  vent.).  At  just  the  same  place  there  are  still  other  decussating 


70  ANATOMY    OF    THE    CENTRAL   NERVOUS    SYSTEM. 

fibers;  namely,  fibers  from  the  anterior  horn  of  one  side  to  the  anterior  root 
of  the  opposite  side;  also  in  mammals  more  central  tracts. 

Among  bony  fishes  and  in  part,  also,  among  selachians,  the  individual 
elements  of  the  commissura  ventralis  are  so  far  divided  that  one  may  often 
recognize  two  quite  distinct  commissures.  In  the  midst  of  the  gray  sub- 
stance one  may  see  everywhere  long  fascicles  of  medullated  nerves  passing 
upward  and  downward.  In  part  these  nerves  are  elongated  fascicles  from 
the  roots,  in  part  derivatives  of  the  commissural  cells,  and  in  part  fibers  from 
other  sources.  Among  cyclostomes  and  some  of  the  bony  fishes  there  are  so 
many  of  these  that  it  is  not  possible  to  trace  a  sharp  line  of  division  between 
the  gray  matter  and  the  peripheral  white  matter. 

But  in  most  vertebrates  we  find  the  central  gray  matter  of  the  spinal 
cord  surrounded  by  white  fibrous  tracts.  The  spaces  in  the  H  (or  X)  which 
represent  the  outline  of  the  gray  may  be  named  as  follows:  Dorsal  or 
posterior  tracts,  ventral  or  anterior  tracts,  and  lateral  tracts.  That  the 
posterior  tracts  are  mostly  or  entirely  formed  from  ascending  or  descending- 
fibers  of  the  posterior  roots  has  already  been  mentioned.  In  the  lateral  and 
anterior  tracts  we  must  look  for  those  fascicles  which  arise  from  the  com- 
missural cells  and  which  bring  into  association  different  levels  of  the  cord. 
These  are  usually  called,  in  brief,  the  tracts  of  the  cord. 

In  most  vertebrates,  even  as  low  as  the  fishes,  there  lie  very  long  tracts 
in  the  anterior  column.  In  fishes  and  larval  amphibians  one  may  find,  close 
beside  the  gray  matter,  one  or  more  very  thick  fibers:  Mauthner's  Fibers. 
Arising  in  the  cranium,  near  the  origin  of  the  eighth  nerve — the  nerve  of 
equilibration — from  gigantic  ganglion-cells,  the  axis-cylinder,  surrounded 
by  enormous  medullary  sheaths,  may  be  traced  as  far  as  the  caudal  vertebrae, 
where  they  emerge  with  the  last  sacral  nerves  (Fritsch).  When  one  recalls 
the  importance  of  the  caudal  musculature  in  the  maintenance  of  equilibrium 
in  swimming  animals,  he  will  recognize  that  the  musculature  in  question  is 
in  special  relation  with  the  nerves  of  the  ampulla.  The  apparent  absence 
of  these  fibers  from  many  eel-like  fishes  (Haller)  depends  upon  the  different 
method  by  which  that  form  of  body  maintains  its  equilibrium.  In  Fig.  29 
these  fibers  are  designated  as  Fibres  Acustico-sacrales. 

Thus  far  the  spinal  cord  has  been  represented  as  an  independent  center. 
As  is  well  known,  it  is  able  to  function  as  such  under  many  circumstances; 
all  experiments  on  decapitated  animals  show  this.  They  teach  that  in  the 
spinal  cord  are  not  only  tracts  for  the  simpler  reflexes,  but  that  even  very 
complicated  movements  may  be  innervated  from  the  spinal  centers  and  be 
brought  into  activity  reflexly.  When  the  decapitated  snake  winds  itself 
about  the  proffered  support;  when  the  decapitated  duck  swims;  or  the 
decapitated  rabbit  is  able  to  make  several  normal  leaps,  it  is  not  to  be 
otherwise  accounted  for  than  that  there  are  in  the  spinal  cord  complete 


STRUCTURE    OF   THE    SPIXAL   CORD.  71 

mechanisms  for  producing  the  movements  which  in  life  were  repeated  num- 
berless times.  In  the  experiments  cited  these  mechanisms,  once  stimulated 
to  activity,  perform  simple  or  successive  combinations  of  movements  in  an 
exactly  'normal  way. 

The  stimuli  which  reach  the  spinal  cord  from  without — i.e.,  those  which 
reach  it  through  the  sensory  nerves — are  alone  sufficient  to  produce  much 
that  was  formerly  supposed  to  be  possible  only  through  higher  psychical 
processes. 

The  activity  of  the  spinal  cord  can  be  influenced,  regulated,  inhibited, 
or  stimulated  by  other  parts  of  the  central  system.  Let  us  consider,  for  a 
moment,  those  tracts  which  are  adapted  to  exert  the  enumerated  influences 
upon  the  activity  of  the  cord. 

The  author's  own  investigations  justify  the  statement  that  from  the 
selachians  and  bony  fishes  to  the  mammals  a  few  tracts  are  constant.  In  the 
first  place,  the  spinal  cord  is  always  in  communication  with  the  cerebellum. 

The  Tractus  cerebello-spinalis  in  mammals,  probably  also  in  birds  and 
reptiles,  lies  in  the  periphery  of  the  lateral  column.  In  fishes  the  author 
has  traced  it  posteriorly,  but  did  not  clearly  make  out  its  location  in  the 
columns  of  the  spinal  cord.  There  is,  however,  ground  for  the  opinion  that 
here,  also,  they  lie  in  the  lateral  column  and  may  be  recognized  again  in  the 
thick  fibers  which  are  to  be  seen  in  the  lateral  columns  of  the  spinal  cord  of 
Gymnotus  (Fig.  31). 

Then  there  is  always  found  a  tract  which  arises  from  the  depths  of  the 
Thalamencephalon  and  passes  to  the  anterior  columns.  It  has  long  since 
been  known  in  the  mammals,  where  it  receives  the  name  Fasciculus  longi- 
tudinalis  posterior  (Fig.  44). 

Finally  it  may  be  accepted  as  highly  probable  that  a  large  tract  which 
arises  in  the  roof  of  the  Mesencephalon,  in  the  tectum  opticum,  passes  into 
the  anterior  lateral  column.  In  these  fibers,  which  in  fishes  and  birds  are 
especially  numerous  at  their  place  of  origin,  one  has  probably  to  deal  with  a 
central  sensory  tract.  At  its  origin  it  is  called  deep  midbrain-marrow,  in 
its  later  course  it  is  called  the  fillet,  or  lemniscus.  In  the  spinal  cord  one  may, 
Avith  all  certainty,  recognize  that  fibers  arise  from  this  fillet  where  sensory 
nerves  end.  They  arise  from  those  cells  around  which  the  nerve-roots  from 
the  posterior  ganglia  ramify.  It  was  possible,  also,  to  demonstrate,  regard- 
ing the  spinal  cord,  that  for  those  cells  in  the  gray  substance  around  which 
the  dorsal  roots  ramify  axis-cylinders  arise  which,  after  decussation  in  the 
ventral  commissure,  pass  toward  the  brain  in  the  anterior  and  lateral 
columns.  These  fibers  arising  from  commissural  cells  are  not  yet  with  cer- 
tainty to  be  differentiated.  It  is,  however,  probable,  on  clinical  and  experi- 
mental grounds,  that  there  is  a  crossed  sensory  tract  in  the  lateral  columns, 
though  the  conclusive  anatomical-  demonstration  of  it  is  not  yet  accom- 


72  ANATOMY   OF   THE    CENTRAL   NERVOUS    SYSTEM. 

f 

plished.  The  secondary  sensory  tract, — i.e.,  tract  of  the  second  order, — 
which  arises  from  the  cells  of  the  gray  matter  and  passes  toward  the  brain 
in  the  antero-lateral  column,  is,  in  all  probability,  a  part  of  the  fillet,  ending 
in  the  roof  of  the  midbrain.  The  complete  system  will,  in  future,  be  called 
the  Tractus  tecto-spinalis  in  the  cord  and  Tractus  tedo-bulbaris  where  it 
comes  into  relation  with  the  medullar  or  bulbar  nuclei. 

In  mammals  there  are,  associated  with  those  above  mentioned,  still 
other  tracts.  Of  these  the  most  important  of  all  is  the  tract  from  the  cere- 
bral cortex:  Tractus  cortico-spinalis.  This  tract,  as  yet  demonstrated  only 
in  mammals,  has  a  different  position  in  the  cord  in  different  species.  It  has 
been  longest  known  in  the  human  anatomy  as  the  pyramidal  tract  of  the 
lateral  column,  or  crossed  pyramidal  tract.  In  the  mouse  and  guinea-pig  it 
lies  in  the  posterior  columns  quite  near  the  commissura  dorsalis.  In  the  dog 
and  in  all  apes  it  lies  in  the  dorsal  segment  of  the  lateral  columns.  In  man 
a  part  of  the  tract  passes  also  in  the  anterior  columns.  This  part  is,  in  man, 
more  highly  developed  than  in  any  other  mammal;  in  the  lower  mammals, 


Fig.  35. — A,  Spinal  cord  of  a  dog  whose  Tr.  cortico-spinalis  has  degenerated 
in  consequence  of  removal  of  the  cerebrum.  B,  Human  spinal  cord  in  which  the 
anterior  and  lateral  pyramidal  tracts  (Tr.  cort.-spin.  lat.  et  Tr.  cort.-spin.  ant.) 
have  suffered  degeneration  in  consequence  of  a  hemorrhage  in  the  left  cerebral 
hemisphere. 


in  fact,  this  part  of  the  tract  is  represented  by  only  a  few  fibers.  This  part  is 
called  the  anterior  or  direct  portion  of  the  pyramidal  tract,  or  the  column 
of  Tiirck. 

One  has  the  impression  that  these  cortico-spinal  tracts  are  developed  in 
proportion  to  the  measure  in  which  the  cerebral  activity  is  called  into  play 
in  those  functions  of  the  extremities  which  are  in  no  way  instinctive,  but  are 
learned  and  cultivated  by  the  individual.  Fig.  35  shows  a  human  spinal 
cord  in  which  these  tracts  are  functionally  destroyed  through  disease;  also 
a  dog's  spinal  cord  which  has  suffered  a  loss  of  the  corresponding  tracts 
through  removal  of  the  hemispheres.  The  difference  in  the  development  of 
these  tracts  in  man  and  in  the  dog  is  apparent. 

It  has  already  been  stated  that  fibers  pass  from  the  white  substance  into 


STRUCTURE    OF    THE    SPINAL    CORD.  73 

the  gray,  and  that  fibers  from  cells  in  the  gray  matter  join  the  white 
columns.  But  in  amphibians  and  fishes  there  are  other  elements  not  yet 
mentioned.  Numerous  dendrites  pass  from  the  ganglion-cells  out  into  the 
white  substance  and  ramify  there  (see  Fig.  29).  The  same  is  true  in  the 
embryo  of  birds  and  mammals,  but  in  the  adults  of  these  classes  one  seldom 
finds  such  dendrites  in  the  white  matter. 

Finally  it  is  to  be  mentioned  that  in  many  lower  vertebrates  true 
ganglion-cells  are  found  even  in  the  midst  of  the  white  matter.    There  is  a 


Fig.  36. — Sections  of  the  spinal  cord  from  large  individuals  of  representative 
vertebrate  classes.  A,  Section  from  the  crocodile:  G.  Africanus.  B,  Section  from 
the  ostrich:  Struthio  camelits.  C,  Section  from  the  shark:  Mustelus. 


large  group  of  such  cells  in  the  periphery  of  the  dorsal  column  in  Cyclos- 
tomes  and  in  certain  fishes, — the  so-called  "Dorsal  cells";  and  also  near 
certain  motor  roots,  large  ganglion-cells  which  probably  send  their  neurites 
into  the  motor  nerves.  A  noteworthy  condition  which  exists  in  birds  is  still 
to  be  described.  Here  in  the  lumbar  segment  of  the  cord  a  tissue-mass 
wedges  itself  in  between  the  dorsal  columns,  pushing  these  so  far  asunder 
that  it  was  formerly  believed  to  be  a  true  bifurcation:  Sinus  rhomboidalis. 


74  ANATOMY   OF   THE    CENTRAL   NERYOTJS    SYSTEM. 

It  is  evident  that  the  elements  which  comprise  the  columns  of  the 
spinal  cord  are  of  very  different  origin.  That  cannot  be  inferred  from  a 
simple  view  of  the  cross-section.  If  one  is  to  have  even  a  general  idea  of  the 
relations,  it  is  at  least  necessary  in  every  case  to  make  a  careful  comparison 
of  many  cross-sections  and  longitudinal  sections.  But,  to  gain  a  clear  con- 
cept of  the  relations,  an  extended  study,  aided  by  embryological  and  other 
methods,  is  necessary. 

Those  who  are  acquainted  with  the  human  spinal  cord  only  are  sur- 
prised at  the  great  size  of  the  spinal  cord  frequently  observed  in  lower  verte- 
brates. The  spinal  cord  is,  in  these  cases,  a  quite  independent  organ,  whose 
size  depends  essentially  upon  the  area  which  is  to  be  supplied  with  spinal 
nerves  and  only  in  very  small  measure  upon  the  development  of  the  parts 
of  the  central  nervous  system.  In  the  lower  vertebrates  it  receives  only  a 
few  fibers,  and  even  in  the  higher  vertebrates  not  many  fibers  from  the  more 
anteriorly  located  parts  of  the  brain.  If  one  would  convince  himself  of 
this,  let  him  compare  in  any  large  fish  the  small  size  of  the  brain  with  the 
relatively  enormous  size  of  the  cord.  The  fish  Gadus  ceglefinus  especially 
possess  a  spinal  cord  which  contains  almost  exclusively  spinal  elements  and 
very  few  cerebral.  The  former  are  highly  developed  because  the  extensive 
body-musculature  and  surface  require  a  rich  innervation. 

This  striking  relation  may  be  readily  followed  even  to  the  mammals. 
The  brain  of  the  horse  or  ox  is  much  smaller  than  that  of  man,  but  their 
spinal  cord  is  more  than  twice  as  thick  as  the  human  cord. 

In  this  connection  compare  the  accompanying  sections  (Figs.  35  and 
36)  of  the  spinal  cord  of  representative  vertebrates.  All  are  drawn  to  the 
same  scale  of  magnification. 


CHAPTER   VI. 

THE  OBLONGATA  AND  THE  NUCLEI  OF  THE  CRANIAL  NERVES. 

LET  us  now  turn  our  attention  to  that  part  of  the  central  nervous 
system  which  supplies  the  region  of  the  head  with  nerves.  Eemember  that 
the  trunk  portion  of  the  nervous  system — the  spinal  cord — represents  a 
more  or  less  independent  center,  joined  to  the  cephalic  segment  through 
several  tracts  varying  among  different  classes  of  animals;  that  an  animal 
can  live  and  can  make  approximately  normal  movements  after  the  spinal 
cord  has  been  completely  severed  from  the  cephalic  part  of  the  central 
nervous  system.  Indeed,  if  the  cephalic  portion,  which  contains  im- 
portant nerves  for  respiration  and  circulation,  remains  intact,  and  if 
the  animal  be  protected  from  certain  damaging  conditions  which  mani- 
fest themselves  under  such  circumstances,  its  existence  will  not  be  inter- 
rupted through  the  complete  loss  of  the  trunk  portion.  This  is  true  even 
for  mammals  (Goltz);  for  lower  vertebrates  it  is  probable  that  even  the 
cephalic  portion  also  may  remain  functionless  for  a  certain  period  without 
causing  death. 

We  come  now  to  the  consideration  of  the  complex  of  nerve-centers 
which  are  associated  with  those  already  described  and  which  are  not  physio- 
logically dependent  upon  them,  though  they  may  be  influenced  by  them  or 
may,  in  turn,  influence  them. 

At  the  cephalic  end  of  the  spinal  cord  one  may  notice  both  macroscop- 
ically  and  microscopically  marked  changes  of  structure;  the  spinal  cord 
merges  into  the  Medulla  OUongata.  These  changes  are  with  slight  varia- 
tions similar  in  all  classes  of  vertebrates;  but,  among  the  lower  vertebrates 
in  which  the  branchial  region  is  to  be  supplied  with  especially  large  nerves, 
the  changes  are  much  more  apparent  and  clear  than  among  mammals. 

One  always  observes  that  the  posterior  columns  diverge  from  each  other 
and  that  the  commissura  dorsalis,  just  below  them,  and  the  adjacent  gray 
substance  about  the  central  canal  are  visible.  The  dorsal  closure  of  the 
central  canal  of  the  nervous  system  is  effected  by  only  a  thin  membrane. 
Passing  anteriorly  from  the  point  of  divergence  of  the  posterior  columns 
this  membranous  roof  becomes  wider  and  wider  with  the  continued  diver- 
gence of  the  columns.  The  widened  central  canal  is  the  fourth  ventricle, 
and  the  membranous  roof — the  Tela  chorioidea  posterior — merges  anteri- 
orly into  the  Formatio  cerebelli. 

(75) 


76  ANATOMY   OF   THE    CENTRAL   NERVOUS    SYSTEM. 

Besides  the  changes  above  noted  the  nervous  system  is  much  greater 
in  cross-section  through  the  medulla  than  at  any  point  posterior  to  that. 
This  may  be  attributed  to  two  circumstances:  (1)  the  appearance  of  the 


Fig.  37. — Sagittal  section  of  an  amphibian  brain  a  little  to  one  side  of  the 
median  plane.  Note  the  continuity  of  the  Tela  chorioidea  posterior  with  the 
cerebellum.  Note,  also,  the  ample  folds  of  the  Tela,  indicating  that  its  surface 
is  much  greater  than  necessary  to  cover  the  fourth  ventricle.  Med.  spin.,  Spinal 
cord.  NacJih.,  Medulla  oblongata.  Hinterhirn,  Floor  of  cerebellum  (pons). 

Formatio  reticularis,  an  "association-system"  of  short  fibers,  which  is  to  be 
met  at  any  point  between  the  spinal  cord  and  the  base  of  the  Thalamen- 
cephalon,  but  which  is  especially  developed  here;  (2)  the  presence  of  nerve- 
centers.  Within  the  skull  there  arise  within  a  very  short  space  three  very 


Fig.  38. — Brain  of  Gadus  ceglefinus.    Those  parts  which  do  not  belong  directly 
to  cranial  nerves  are  shaded. 


large  nerves:  the  Vagus,  the  Acusticus,  and  the  Trigeminus.  Where  they 
take  their  origins — i.e.,  at  the  location  of  the  nuclei — the  central  organ  is 
naturally  much  enlarged.  The  rich  cerebral  and  cerebellar  connections  to 
such  nerve-centers  also  add  not  a  little  to  the  volume  of  the  medulla. 


THE    OBLONGATA   AXD    THE    NUCLEI    OF   THE    CRANIAL    NERVES. 


77 


One  usually  has  little  conception  of  the  great  size  of  those  parts  of  the 
central  nervous  system  which  are  in  connection  with  the  cranial  nerves 
among  lower  vertebrates.  In  the  brain  of  the  fish  Gadus  ceglefinus  (Fig.  38) 
the  nerve-roots  alone  aggregate  a  much  greater  mass  than  that  part  of  the 
brain  not  in  relation  to  the  nerves  in  question. 

Sections  through  the  medulla  of  fishes  show  that  this  is,  for  the  most 
part,  simply  the  origin  of  the  great  cranial  nerves.  All  other  systems  of 
fibers  are,  compared  with  these,  quite  in  the  background.  There  exist  also 
within  the  medulla  several  special  centers  which  are  in  relation  with  the 
cerebellum  and  with  the  acusticus. 

Finally,  it  is  to  be  mentioned  that  this  part  of  the  nervous  system  is 


Fig.  39. — Dorsal  view  of  the  Oblongata  and  cerebellum  of  the  sturgeon: 
Acipenser  ruthenus.  The  Tela  is  dissected  off  and  lies  at  the  left  Note  the 
large  nuclei  of  the  N.  trigeminus,  the  N.  acusticus,  and  the  N.  vagus.  (After 
Goronowitsch.) 


traversed  by  those  tracts  which  pass  to  the  spinal  cord  from  the  regions 
anterior  to  it,  as  well  as  fibers  from  the  same  source  destined  for  the  medulla 
itself. 

These  notable  changes  which  appear  at  the  cephalic  end  of  the  spinal 
cord  are  still  more  apparent  on  cross-sections  than  in  the  outer  form. 

It  may  be  best  to  choose  as  the  first  object  for  observation  the  medulla 
of  the  amphibian  larva,  because  of  its  simple  structure  and  its  gradual 
differentiation  from  the  cord  (see  Fig.  40). 


78 


ANATOMY   OF   THE    CENTRAL    NERVOUS    SYSTEM. 


Here  the  gray  matter  is  constructed  almost  exclusively  of  that  heaping- 
up  of  neuroblasts  of  which  mention  was  made  while  discussing  the  em- 
bryonic development.  In  section  A  of  the  figure  one  recognizes  the  anterior 
and  posterior  columns  of  the  spinal  cord;  but,  since  the  section  is  from 
the  cervical  region,  it  is  noticeable  that  the  dorsal  columns  touch  a  much 
greater  part  of  the  periphery  than  is  true  at  a  lower  level. 

In  section  B  the  posterior  horns  diverge  from  each  other  and  the  dorsal 
epithelium  of  the  central  canal  is  used  to  form  the  Tela  chorioidea. 


Fig.  40. — Four  sections  through  the  medulla  of  a  four-centimeter  larva 
of  Salamandra  maculata. 


Now,  on  either  side  of  the  ventricle  lie  gray  masses,  destined,  like  the 
posterior  horns  (col.  dors.),  to  receive  sensory  nerves.  In  figure  C  such  a 
nerve — the  Vagus,  which  enters  here — is  represented. 

Note,  at  the  same  time,  the  increase  of  the  posterior  gray  column  (col. 
dors.)  as  the  point  of  entrance  of  the  Vagus.  Still  farther  above,  at  D,  the 
great  Acusticus  enters  with  one  of  its  roots;  and  now  one  sees  the  relations 
of  the  spinal  cord  quite  changed;  but  a  single  glance  backward  of  the  figures 


THE  OBLOXGATA  AND  THE  XUCLEI  OF  THE  CEAXIAL  NEEVES.     79 

reveals  to  which  portion  of  the  gray  matter  the  lateral  margin  of  our  prepa- 
ration corresponds. 

The  anterior  horns  of  the  spinal  cord  are  no  longer  clear  in  B;  hut 
here,  and  even  better  in  C,  note  that  fibers  still  arise  from  them.  In  section 
A  they  have  given  off  the  left  cervical  nerves  functioning  as  Hypoglossus. 
In  C  they  send,  also,  dorsal  motor  fibers,  which  turn  to  make  the  motor 
roots  of  the  Vagus.  The  cell-column  of  the  anterior  horn  remains  intact 
for  a  greater  distance;  higher  up  the  motor  fibers  of  the  Facialis  arise;  also 
those  which  join  the  Trigeminus.  In  the  nucleus  of  the  Facialis  we  have 
probably  to  do  with  another  cell-group  than  that  in  the  nucleus  of  the 
Vagus. 

Let  us  now  turn  to  a  more  complicated  section  on  which  may  be  demon- 
strated several  of  the  especially  important  relations  of  the  beginning  of  the 
medulla. 

Fig.  41  presents  a  section  through  the  lower  end  of  the  medulla  of 
CephalopUra,  a  large  ray.  Note  the  ventral  columns,  or  anterior  horns, 
from  which  arise  nerves.  The  most  anterior  pair  of  cervical  nerves,  which 
supply  about  the  same  region  that  in  higher  animals  is  innervated  by  the 
twelfth  pair  of  cranial  nerves, — the  Hypoglossus, — arises  just  like  other 
spinal  nerves. 

The  dorsal  columns  (posterior  horns)  are  still  to  be  seen,  but  it  is 
already  difficult  to  trace  their  resemblance  to  the  typical  ones  previously 
described.  They  are  much  broader  and  changed  to  a  looser,  net-like,  gray 
substance,  upon  which  rests  a  striking  crescent-shaped  nucleus  (Fig.  41, 
Fun.  post.).  The  appearance  of  this  long,  trough-shaped  structure,  which 
reaches  far  up  under  the  cerebellum,  is  characteristic  for  the  upper  spinal 
cord  and  the  medulla.  Higher  magnification  demonstrates  that  this  note- 
worthy nucleus  receives  along  its  whole  course  fine  fibers  from  the  surround- 
ing mass  of  fibers;  and  when  one  follows  them  upward  one  can  trace  them 
to  the  place  where  the  Trigeminus  courses  from  the  Gasserian  ganglion  into 
the  brain.  Now,  for  the  first  time,  one  recognizes  with  what  he  is  dealing: 
a  great  fascicle  from  the  sensory  nerve,  which  passes  from  the  ganglion 
down  into  the  cord  to  end  in  the  above-described  nucleus.  This  fascicle 
is,  called  the  Radix  spinalis  Trigemini;  the  nucleus  at  the  end  of  the  dorsal 
horn  is  its  terminal  nucleus:  Substantia  gelatinosa  Rolandi  (Fig.  41,  Nucl. 
N.  V.).  On  the  median  side  of  this  nucleus  lie  fibers  from  the  posterior 
columns  (Fun.  post.).  They  inclose,  in  turn,  gray  masses,  located  where  in 
the  cord  the  posterior  columns  lie,  here  called  nuclei  of  the  posterior  col- 
umns (nucl.  fun.  post.).  In  birds  and  mammals  the  existence  of  nuclei  into 
which  a  considerable  part  of  the  posterior  columns  enter  is  established 
beyond  doubt,  as  will  be  shown  later;  but  in  fishes  and  amphibia  it  is  not 
absolutely  certain  that  a  similar  condition  exists.  In  the  Cephaloptera  it  is, 


80 


ANATOMY   OF   THE    CENTRAL   NERVOUS    SYSTEM. 


therefore,  with  some  hesitation  that  I   designate  this  structure  as  the 
"nucleus  of  the  posterior  columns." 

But  the  greatest  difference  between  this  section  and  one  of  a  typical 
spinal  cord  is  the  fact  that  in  the  space  between  anterior  and  posterior  horns 
innumerable  commissural  cells  have  made  their  appearance,  cells  whose 
large  neuraxons,  arranged  in  small  fasciculi,  pass  upward  through  the 
medulla  even  into  the  Mesencephalon  and  Thalamencephalon.  This  is  prob- 
ably a  great  system  of  association-fibers  which  connect  certain  levels  of  the 
cranial  segment  of  the  central  system  to  each  other  and  with  the  anterior 
end  of  the  spinal  cord.  This  system,  which  is  similarly  located  in  all  ani- 
mals, is  characteristic  of  the  Medulla,  and  is  well  adapted  to  be  the  organ 


Fig.  41. — Section  through  the  medulla  oblongata  of  a  Ray: 
the  Cephaloptera  lumpus. 


of  those  most  intimately  co-ordinated  functions  whose  seat  is  in  the  Medulla. 
In  the  figure  this  region  is  designated  as  Tractus  Irevis. 

Without  doubt  we  have  to  deal  here  with  an  increase  of  that  structure 
already  described  with  the  spinal  cord  as  the  cellulae  commissurales  and  the 
tracts  arising  from  them.  As  in  the  spinal  cord,  so  here  there  exist  fibers 
of  short  course,  crossed  and  uncrossed.  The  ventral  commissure,  small  in 
the  spinal  cord,  naturally  becomes  much  increased  incident  to  the  increase 
of  the  whole  system.  It  is  known  from  this  point  up  to  the  Corpora  Quad- 
rigemina  as  the  raphe  decussation.  Within  this  decussation,  as  in  the 
spinal  cord,  are  cross-fibers  of  other  categories  than  those  which  arise  from 
the  cellule  commissurales.  But  these  will  be  described  later. 

The  area  of  association-fibers — i.e.,  the  Tr.  brevis  of  the  oblongata — is 
just  as  well  developed  in  the  lowest  vertebrates  as  in  the  highest  representa- 


THE  OBLONGATA  AND  THE  NUCLEI  OF  THE  CRANIAL  NERVES.     81 

tives  of  that  branch.  In  this  connection  compare  Fig.  41  with  Fig.  230 
(Processus  reticularis).  It  is  evident  that  we  have  here  to  deal  with  the 
anatomical  basis  of  very  similar  functions.  Through  this  tract  of  associa- 
tion-fibers the  fibers  which  pass  from  the  spinal  cord  to  the  cerebellum,  the 
Mesencephalon,  and  the  Thalamencephalon  are  pushed  laterally  toward  the 
periphery.  Note  in  Fig.  41  the  location  of  the  Tr.  cerebello-spinales  and  the 
Tr.  tecto-thalamo-spinales. 

The  Tr.  tecto-spinales  contain,  as  was  previously  shown,  crossed  tracts 
from  the  terminal  nuclei,  into  which  the  sensory  fibers  of  spinal  roots 
enter.  They  are,  indeed,  a  secondary  sensory  tract  from  those  nuclei  to  the 
roof  of  the  Mesencephalon.  In  the  medulla  they  are  joined  by  the  much 
larger  bundle  from  the  terminal  nuclei  of  the  cranial  nerves  and  the  now 
much  enlarged  bundle,  which  may  be  subdivided  into  numerous  parts 
properly  designated  by  the  term  Tr.  tecto-spinales  et  bulbares,  or  more 
briefly  the  English  name  FILLET.  The  Fillet  undergoes  a  further  increase 
in  the  medulla.  It  comes  from  the  nuclei  of  the  spinal  and  cranial  nerves 
of  the  opposite  side.  Be.ar  in  mind  that  in  many  vertebrates  a  large  part  of 
the  posterior  root-fibers  does  not  end  in  the  gray  horns,  but  ascends  to 
the  medulla  in  the  posterior  columns.  It  enters  the  nucleus  of  the  pos- 
terior column,  which  replaces  the  column  at  the  lower  end  of  the  medulla. 
In  birds  and  mammals  in  which  the  nucleus  is  very  large  one  may  de- 
termine with  certainty  that  from  this  nucleus  a  system  of  arcuate  fibers 
arise,  which  traverse  the  medulla  to  the  raphe,  cross  to  the  other  side, 
and  join  the  Tr.  tecto-spinales  et  tecto-bulbares,  which  pass  toward  the 
brim  on  either  side  of  the  median  line. 

The  fibers  in  question — Fibrce  arcuatce  internee  medulla — are  nothing 
else  than  a  secondary  tract  from  the  points  where  the  posterior  root-fibers 
end.  They  are  the  last  of  the  sensory  nerves  to  cross  to  the  opposite  side  of 
the  central  system  and  unite  with  those  that  crossed  in  the  spinal  cord. 

The  fillet,  or  Lemniscus,  thus  increased  occupies  a  large  field  in  the 
ventral  and  lateral  part  of  the  medulla. 

,.  So  we  have  to  deal  here  with  tracts  which,  coming  from  the  midbrain, 
reach  the  termination  of  the  sensory  spinal  nerves  by  crossing  to  the  opposite 
side  of  the  medulla  as  arcuate  fibers.  Keep  this  in  mind,  for  in  the  medulla, 
where  the  nerves  have  such  large  nuclei,  we  shall  frequently  find  such 
arcuate  fibers  and  be  able  to  trace  them  into  the  fillet. 

In  the  oblongata  of  the  adult  Triton  (Fig.  42),  which  is  chosen  because 
it  is  closely  related  to  the  salamander  larva  shown  above,  you  see  the 
arcuate  fibers  from  the  region  of  the  nucleus  of  the  posterior  columns  well 
developed,  and  you  recognize  also,  that  they  pass  to  an  area  on  either  side 
of  the  middle  line,  which  is  filled  with  severed  fibers,  while  many  of  them 
cross  to  the  opposite  side  in  a  ventral  decussation.  It  is  not  usually  possible 


82  ANATOJIY    OF    THE    CEXTEAL    NERVOUS    SYSTEM.     . 

to  follow  the  whole  course  in  a  single  section;  thus  the  accompanying 
figure  barely  shows  the  relation  between  the  arcuate  fibers  and  the  decussa- 
tion. 

With  this  survey  of  the  more  important  constituents  in  the  cross- 
section  of  the  lower  end  of  the  medulla,  it  will  be  easy  to  understand  the 
opposite  figure  (Fig.  43),  which  shows  a  similar  section  from  the  medulla  of 
an  alligator. 

But  what  of  the  fibers  of  the  anterior  columns  which  were  found  in 
the  spinal  cord?  In  the  section  of  the  medulla  of  the  ray  (Fig.  41),  they 
occupy  exactly  the  same  position  as  in  the  spinal  cord.  A  part  of  these 
fibers  pass,  indeed,  into  the  fillet,  but  most  of  them  form  a  thick  column, 
very  striking  in  most  sections,  which  maintains  the  same  location  through 
the  oblongata,  even  increasing  in  volume.  This  tract — the  Fasciculus 


Fig.  42. — Cross-section  through  the  Oblongata  of  a  mature  Triton. 


longitudinalis  posterior — may  be  followed  to  the  base  of  the  Thalamen- 
cephalon.  It  appears  to  receive  fibers  from  all  motor  nuclei  throughout  its 
long  course.  Degeneration  experiments  on  mammals  teach  that  the  fibers 
are,  for  the  most  part,  short  ones.  In  fishes,  amphibia,  and  reptiles  this 
fasciculus  is  one  of  the  largest  of  the  medulla.  It  occupies  the  whole  floor 
of  the  fourth  ventricle,  as  you  see  in  the  sturgeon  (Fig.  39). 

In  the  midst  of  this  tract  in  aquatic  animals  are  the  previously 
described  thick  fibers — Fibres  acustico-spinales — from  the  acustieus  region 
to  the  caudal  musculature.  These  fibers  may  be  seen  in  Figs.  40  and  42, 
Fig.  40  D  showing  the  decussation  and  the  large  terminal  cell  (cellula  M. 
Fas.)  from  which  on  either  side  the  fiber  arises. 

We  have  now  located  in  the  medulla  most  of  the  tracts  previously 
known  in  the  cord.  One  important  tract  remains  yet  to  mention:  the  Tr. 


THE    OBLOXGATA   AXD    THE    NUCLEI    OF    THE    CEAXIAL    XTERVES. 


S3 


cortico-spinalis.  This  tract  is  present  only  in  mammals,  and  will,  therefore, 
be  specially  treated  later  under  the  description  of  the  mammalian  brain.  It 
may  be  stated  here,  however,  that  its  fibers  begin  in  the  medulla,  for  the 
most  part  decussate,  and  then,  as  two  large  columns, — the  Pyramids, — lie 
ventral  to  the  anterior  columns  and  the  fillet,  making  there  a  simple  addition 
to  the  picture  which  has  already  been  presented.  Frequently  a  child  is 
born  without  a  cerebrum,  and  it  lacks,  therefore,  the  pyramidal  columns, 
and  its  medulla  is  similar  to  that  of  the  other  classes  of  vertebrates. 

One  meets  these  fiber-systems  in  all  sections  of  the  medulla  farther 
toward  the  brain,  until  the  cerebellar  tract  turns  toward  the  cerebellum 
and  the  spinal  portions  of  the  cranial  nerves  pass  out  of  their  respective 
roots.  Furthermore,  bundle  after  bundle  from  the  processus  reticularis 


Fig.  43. — From  the  caudal  end  of  the  Oblongata  of  Alligator  lucius.  Note 
the  origin  of  the  Hypoglossus  (N.  XII)  from  the  anterior  horn  (co?.  ventr.)  and 
the  terminal  nucleus  of  the  Trigeminus  (nucl.  term.  N.V.  spin.),  dorso-lateral 
to  which  lies  the  Trigeminus  root  (Rod.  spin.  V).  Note,  also,  the  nucleus  of 
the  posterior  columns  (nucl.  f.  dors.),  in  which  the  fasciculus  from  the  posterior 
root  ends  (Fun.  dors.).  Further  study  of  the  figure  will  reveal  many  features 
already  discussed. 


(Associations-feld)  of  the  medulla  ends,  and  bundle  after  bundle  arises  to 
end  farther  forward.  However,  the  section,  as  a  whole,  varies  little  as  to 
the  parts  already  described. 

But  another  factor  causes  very  marked  changes  in  the  structure  of 
the  medulla  as  one  studies  sections  near  the  brain;  namely,  the  nuclei  of 
the  cranial  nerves  and  the  arcuate  fibers,  which  pass  into  these  from  the 
fillet  and  from  the  cerebellum. 

The  study  of  the  nuclei  of  the  cranial  nerves  in  the  medulla  speaks 
conclusively  for  the  position  already  taken  that  there  is  in  the  animal  king- 


84  ANATOMY    OF    THE    CENTRAL    NEKVOUS    SYSTEM. 

dom  no  such  thing  as  a  brain  which  is  throughout  of  a  higher  or  lower 
degree  of  development.  Xow  here,  now  there,  certain  parts  of  the  brain 
are  more  developed,  and  this  development  depends  in  no  way  upon  the 
position  of  the  animal  in  the  phylogenetic  series,  but  solely  upon  require- 
ments: i.e.,  upon  the  somatic  characteristics  which  the  animal  has  acquired 
in  this  or  that  region. 

You  will  find  that  the  bony  fishes  possess  an  exceedingly  simple  brain, 
which  is  not  at  all  to  be  compared  with  that  of  man.  But  these  animals 
possess  not  only  much  larger  terminations  for  the  optic  nerves  than  does 
any  mammal,  but  the  nerve-nuclei  in  its  medulla  have  such  a  development 
and  such  complicated  relations  that  the  same  structures  in  reptiles,  birds, 
and  mammals  seem,  in  comparison,  very  small  and  simple. 

Thus  the  anatomical  picture  of  the  medullar  nuclei  of  the  cranial 
nerves  varies  much  in  the  animal  kingdom.  I  will,  therefore,  try  to  present 
a  few  facts  which  are  common  to  all. 

Let  us  divide  the  cranial  nerves  in  question  into  two  groups:  a  posterior 
group,  including  the  Hypoglossus,  the  Accessorius,  the  Vagus,  and  the 
Glosso-pharyngeus;  and  an  anterior  group,  including  the  Facialis,  the  Acus- 
ticus,  and  the  Trigeminus. 

If  one  views  the  cranial  nerves  only  from  the  stand-point  of  the  rela- 
tions of  their  deep  origin,  one  finds,  throughout  the  whole  animal  kingdom, 
an  astonishing  similarity.  For  example,  the  terminal  nuclei  for  the  cranial 
nerves  are,  in  fishes  and  mammals,  located  the  same.  They  vary  consider- 
ably, however,  in  the  way  in  which  the  roots  leave  the  central  system.  Sub- 
sequent to  the  origin  of  the  nerves  there  takes  place  the  most  varying  com- 
binations of  the  root-fibers;  so  that  the  certain  tracing  of  them  to  the 
surface  of  the  brain  is,  in  the  lower  vertebrates,  a  task  on  which  comparative 
morphology  is  still  at  work.  For  example,  the  Facialis  is  sometimes  so 
mixed  with  the  fibers  of  the  Trigeminus  that  it  is  only  in  the  distribution 
at  the  periphery  that  it  may  be  differentiated  from  that  nerve. 

The  ventral  columns  of  large  ganglion-cells  have  been  located  as  the 
origin  of  the  motor  nerves  of  the  spinal  cord.  This  cell-column  may  be 
demonstrated  from  the  sacral  region  to  the  medulla.  It  consists  of  a  series 
of  nerve-nuclei  between  which  lie  commissural  cells.  It  is  advisable  to 
separate  this  column  into  two  series:  a  more  ventral  one  (Anterior-horn  zone 
of  His)  and  a  more  lateral  one  ("Lateral-horn  zone").  From  the  first  arise 
the  Hypoglossus  and  all  of  the  anterior  roots  of  the  spinal  cord  for  the 
trunk-musculature.  From  the  latter  arise  principally  fibers  which  are  de- 
voted to  the  motor  innervation  of  the  viscera,  only  in  the  medulla.  These 
lateral-horn  fibers  become  separated  from  the  anterior-horn  fibers  and  leave 
the  medulla  as  motor  fibers  of  the  Vagus  and  Accessorius.  Farther  down 
the  spinal  cord  they  leave  with  other  fibers  of  the  anterior  roots.  According 


THE  OBLOXGATA  AND  THE  NUCLEI  OF  THE  CRANIAL  NERVES.    85 

to  Gaskell,  the  latter  fibers  enter  a  mixed  spinal  nerve,  while  the  former 
enter  the  Sympatheticus.  The  most  centrally  located  segment  of  the  motor 
columns  produce  from  their  lateral  divisions  the  X.  facialis.  The  masseteric 
branch  of  the  Trigeminus  receives  its  fibers  from  cells  which  belong  to 
both  lateral  and  ventral  divisions  of  the  motor  column. 

The  posterior  horns  of  the  gray  matter  are  also  continued  through  the 
medulla,  where  they  are  encroached  upon  by  the  Vagus,  the  Glosso- 
pharygeus,  the  Acusticus,  and  the  Trigeminus  after  their  origin  from  the 
nuclei.  It  was  noted  in  Trigla  (Fig.  30,  B)  that,  in  the  trunk-segment, 
wherever  the  sensory  nerves  are  especially  strong  the  terminal  nuclei  are 
enormously  hypertrophied.  The  same  is  quite  generally  the  case  with  the 
terminal  nuclei  of  the  large  medullar  nerves.  One  of  these — the  longi- 
tudinally extended  terminal  nucleus  of  the  spinal  root  of  the  Trigeminus — 
has  already  been  described.  "We  have  now  to  do  with  a  tract  which,  from 
its  origin  in  the  Gasserian  ganglion,  passes  far  back,  ending  in  the  cervical 
portion  of  the  spinal  cord.  Such  tracts  are  designated  descending  tracts. 
All  sensory  nerves  of  the  medulla  have  such,  but  in  no  other  case  is  the 
descending  tract  so  large  or  so  well  known  as  in  the  Trigeminus.  Knowing 
that  all  posterior  nerve-roots  after  entering  the  cord  give  off  a  descending 
twig  to  a  part  of  the  gray  horn  lying  farther  posterior,  one  will  not  be  sur- 
prised to  find  a  similar  thing  true  in  the  cranial  nerve-roots  of  the  medulla. 
The  most  posterior  cranial  nerve — the  Hypoglossus — has  already  been  de- 
scribed. It  arises  from  a  cell-group  in  the  anterior  horn  (see  Fig.  43). 

From  the  same  segment  of  gray  matter,  but  from  a  somewhat  laterally 
located  cell-group,  in  reptiles,  birds,  and  mammals,  arise  fibers  which,  pass- 
ing laterally,  leave  the  central  system  as  the  Accessorius  (see  Fig.  43). 

In  the  lower  vertebrates  this  nerve  arises  almost  in  the  same  manner, 
but  its  fibers  usually  pass  higher  and  leave  the  medulla  with  the  Vagus, 
joining  the  motor  part  of  that  nerve.  In  that  case  there  is  no  reason  why 
one  should  not  compare  the  most  posterior  root  of  the  motor  Vagus  with 
the  Accessorius. 

The  Vagus  itself  passes  to  the  dorsal  margin  of  the  medulla  from  the 
Ganglion  jugulare.  It  penetrates  the  fiber-system  that  here  lies  in  its  way 
(i.e.,  the  Fibrse  arcuatas  interns  arising  from  the  nucleus  of  the  posterior 
columns);  also  often  the  ascending  spinal  root  of  the  Trigeminus,  and  ends 
there  in  a  noticeable  enlargement  of  the  gray  matter  belonging  to  the  pos- 
terior columns  farther  back.  This  may  be  readily  seen  in  the  accompanying 
figures  from  the  medulla  of  a  gold-fish. 

In  the  figure  one  notes  that  the  terminal  nucleus  of  the  Vagus  is  rela- 
tively very  large:  it  has  to  receive  a  much  larger  nerve  than  in  other  verte- 
brates. A  veritable  tumor — the  Lobus  nervi  vagi — results  here. 

In  the  brain  of  the  sturgeon  (Fig.  39)  the  nucleus  of  the  Vagus  is 


86 


ANATOMY    OF    THE    CENTRAL    NERVOUS    SYSTEM. 


visible  only  as  an  elongated  prominence,  and  in  birds  and  mammals  it  forms 
only  a  slight  prominence  on  the  floor  of  the  fourth  ventricle  (compare  also 
Fig.  52). 

From  the  ventral  side  fibers  enter  the  vagus  nucleus  which  cross  over 
from  the  opposite  side.     The  decussation  is  so  striking  in  fishes  that  one 


Fig.  44. — Sagittal  section  through  brain,  medulla,  and  upper  cord  of  a  young 
cyprinoid  of  four-centimeters'  length,  showing  the  course  of  the  Fasciculus  longi- 
tudinalis  posterior. 

may  readily  see  its  white  fibers  with  the  unaided  eye.  We  have  to  deal  here 
with  a  fascicle  to  the  fillet.  The  nuclei  of  all  cranial  nerves  possess  such 
(Fig.  45,  Tr.  vago-tect.).  Furthermore,  the  sensory  nucleus  of  the  Vagus 
receives  an  accretion  (especially  large  in  fishes)  from  the  cerebellum  where 
decussation  takes  place. 

In  the  higher  vertebrates,  also,  there  exists  a  vago-cerebellar  tract,  but 


Fig.  45. — Two 
four 


sections  from  the  medulla  of  a  young  gold-fish — Cyprinus  auratus- 
centimeters  long.    Sec.  A  is  the  more  posterior  of  the  two. 


in  mammals  at  least  it  passes  out  with  the  root-fibers  direct.  In  fishes  and 
amphibians  a  part  of  the  fibers  of  the  Vagus  innervate  the  skin  just  like 
sensory  spinal  nerves;  but  in  the  higher  vertebrates  the  sensory  part  of  the 
vagus  contains  only  sensory  nerves  from  the  viscera.  The  Vagus  contains 


THE  OBLOXGATA  AND  THE  XUCLEI  OF  THE  CRAXIAL  XERVES.     87 

also  motor  fibers.  Eecall  that  Fig.  34  shows  fibers  from  the  cells  of  the 
anterior  horn  to  the  sensory  roots.  When  that  figure  was  under  discussion 
your  attention  was  called  to  the  fact  that  we  probably  have  to  deal  here 
with  motor  elements  to  the  visceral  tracts.  To  Gaskell  is  due  the  credit  of 
having  shown  how  the  motor  tracts  for  the  Vagus  differ  in  no  way  from 
those  already  described  for  the  spinal  nerves.  (Compare  Fig.  34  with 
Fig.  46.) 

Just  as  in  the  chicken  the  multipolar  cell  near  the  anterior  horn  sends 
its  neuraxon  out  in  the  posterior  root,  so  the  similarly  located  motor  nucleus 
of  the  vagus  sends  its  neuraxons  to  the  sensory  vagus  root,  which  is  the 
homologue  of  a  posterior  root.  The  motor  vagus  fibers  are  essentially 
equivalent  to  the  motor  fibers  in  the  posterior  root.  They  arise  from  a 
nucleus  which,  in  fishes,  lies  dorsal  to  the  nucleus  of  the  Hypoglossus,  but 


Fig.  46. — Motor  and  sensory  vagus  nucleus  of  Alligator  mississippiensis. 

in  amphibians,  reptiles,  and  birds  lies  ventrolateral  to  this.  To  be  sure, 
the  origin  of  the  vagus  fibers  is  frequently  not  sharply  differentiated  from 
that  of  the  hypoglossus  fibers.  The  nucleus  is  the  motor  nucleus  of  the 
Vagus.  It  sends  root-fibers  to  the  same  and  to  the  opposite  sides.  The 
decussation  takes  place  very  near  the  floor  of  the  fourth  ventricle. 

That  a  part  of  the  vagus  root  as  a  descending  fascicle  ends  in  the  gray 
matter  somewhat  posterior  to  its  entrance  has  been  mentioned. 

In  the  region  of  the  Vagus  a  great  number  of  root-fibers  enter  the 
medulla.  It  is  not  with  certainty  decided  whether  we  are  dealing  here  with 
a  single  nerve  or  with  a  fused  combination.  Only  the  most  anterior  of  the 
sensory  roots  of  the  Vagus,  always  somewhat  separated  from  the  others  at 
the  surface  of  the  medulla,  has  it  been  thought  necessary  to  separate  out  as 
a  distinct  nerve:  the  Glosso-pharyngeus.  This  nerve,  in  all  vertebrates,  arises 
only  in  a  small  part  direct  from  the  gray  matter  of  the  spinal  cord.  A 


88 


ANATOMY   OF   THE    CENTRAL    NERVOUS    SYSTEM. 


greater  part  becomes  at  once  inclosed  in  a  fascicle  with  several  vagus  roots 
and  passes  toward  the  spinal  cord.  Throughout  the  whole  course  as  far  as 
the  first  cervical  nerve  it  is  to  be  traced  as  a  separate  bundle. 

The  Radix  bulbo-spinalis  Vagi  et  Glosso-pharyngei  gradually  buries  itself 
just  like  the  bulbo-spinal  root  of  the  Trigeminus:  in  a  thin  column  of  gray 
matter  which  lies  near  it  throughout  its  whole  course.  That  is  the  bulbo- 
spinal  terminal  nucleus  of  this  nerve.  The  fascicle  is  easy  to  find,  ventral 
from  the  sensory  nucleus  of  the  Vagus. 


Molecular  layer 
Purkinje's  cells 
Granular  layer. 

Nucl.  globes,  cerebelli 


Nucl.  Deiteri 
Nncl.  N.  VHI  Tub.  acusticum 

Tr.  acnst.-cerebellaris 

Nucl.  N.  VIII  dorsal. 

Nncl.  N.  abdncentis 

Nncl.  terminal.  N.  glosso-phar. 

N.  acusticus 

Tr.  bulbo-spin.  N.  V. 

N.  glosso-pharyngeus 

Nucl.  N.  facial  is 

Nucl.oftheraphe 


Fig.  47. — -Region  of  the  entrance  of  the  Glosso-pharyngeus  of  a  young  spar- 
row, in  which  the  development  of  the  medullary  nerve-sheaths  is  not  yet 
complete. 


The  spinal  cord  offers,  especially  in  fishes,  numerous  good  examples  of 
the  fact  (already  cited  in  the  description  of  the  spinal  cord)  that  from  the 
small  primitive  fundaments  are  developed  exceedingly  important  structures 
according  to  the  various  development  of  the  peripheral  organs.  It  is  only 
with  difficulty  that  the  mature  structures  can  be  traced  to  their  origin.  The 
angler-fish — Lophius  piscatorius — possesses,  upon  its  head,  lateral  lines  and 


THE    OBLOXGATA   AXD    THE    NUCLEI    OF    THE    CEAXIAL   XERVES. 


89 


tufts,  innumerable  delicate  leaf-like  appendages  of  the  skin  which  completely 
mask  the  lazy  ambushed  fish,  so  that  it  appears  like  a  flat  stone  overgrown 
with  lichen  and  corals.  Lying  thus  in  the  mud  the  angler  lets  its  worm-like 
decoy  float  above  it.  The  whole  cutaneous  region  involved  in  these  curious 
structures  is,  in  fishes,  supplied  by  the  Vagus  and  Trigeminus.  Fritsch,  to 
whom  we  are  indebted  for  much  of  our  knowledge  of  the  fish-brain,  found 
that  the  nuclei  of  these  nerves  in  Lophius  —  and  in  this  fish  alone  —  were 
supplemented  by  immense  ganglion-cells  which  sent  their  neuraxons  into 
the  nerves.  We  have  to  deal  here,  evidently,  with  hypertrophy  of  the 
dorsal  cells  which  lie  near  the  periphery  of  the  cord.  These  cells  are  so  large 


Fig.  48. — Medulla  of  the  Torpedo.    Section  from  the  region  of  the  vagus  nucleus. 


in  Lophius  that  they  require  for  their  nutrition  separate  little  capillary 
loops,  which  lie  among  the  cells. 

But  still  more  interesting  is  the  much-studied  large  nucleus  which  is 
found  in  the  electric  ray,  far  forward  in  the  floor  of  the  fourth  ventricle, 
projecting  into  its  cavity.  This  nucleus  gives  origin  to  the  electric  nerves, 
one  on  each  side.  This  paired  structure,  frequently  fused  anteriorly,  con- 
tains besides  several  small  multipolar  cells,  a  great  number  of  gigantic  gan- 
glion-cells, which  all  send  their  neuraxons  out  into  the  electric  nerves. 

With  our  present  knowledge  of  the  nuclei  of  the  selachian  brain  it  is 
difficult  to  give  these  structures  a  positive  interpretation,  but  the  prob- 
abilities indicate  strongly  that  we  have  to  deal  here  with  nothing  else  than 


90  ANATOMY    OF   THE    CENTRAL    NERVOUS    SYSTEM. 

an  hypertrophy  of  a  part  of  the  motor  vagus  nucleus.  The  electric  organ 
of  the  Torpedo  is  modified  from  a  part  of  the  head-musculature.  Engleman 
has,  in  fact,  been  able  recently  to  show  how  the  electric  plates  of  the  electric 
organs  develop  directly  from  the  muscle  end-plates  of  the  modified  motor 
nerves. 


CHAPTEE    VII. 

THE   MEDULLA    (Continued). 

AT  the  level  where  the  Glosso-pharyngeus  roots  pass  laterally  to  reach 
the  surface  of  the  medulla  one  may  recognize,  on  the  median  side  of  them, 
a  new  nucleus:  an  acusticus  nucleus. 

This  is  the  region  of  the  origin  of  that  cranial  nerve  whose  relations 
are  least  known  in  the  lower  vertebrates.  The  investigations  of  recent 
years  have  finally  made  the  Acusticus  better  understood  in  mammals.  But 
even  in  birds  and  still  more  so  in  lower  vertebrates  we  have  to  depend  on 
what  may  be  learned  from  sections.  As  yet,  no  one  has  attempted  to  study 
so  extremely  complicated  a  nerve  by  the  degeneration-method  or  the  de- 
velopment-method. But  sections  alone  of  this  level  of  the  medulla  where 
the  structure  is  so  complicated  give,  only  too  easily,  occasion  for  misinter- 
pretations. I  will  at  present,  then,  confine  myself  only  to  that  which  has 
been  with  certainty  established. 

The  Acusticus  always  contains  one  portion  which  passes  to  the  vesti- 
bule and  one  to  the  cochlea.  The  first,  which  supplies  the  labyrinth,  is,  as 
numerous  experimenters  have  demonstrated,  of  especial  importance  for  the 
maintenance  of  the  equilibrium  of  the  body.  Ewald's  experiments  have 
shown  how  every  fluctuation  of  the  fluid  "of  the  lymph  leads,  through  the 
agency  of  this  nerve,  to  the  disturbance  of  the  equilibrium.  They  have 
also  proved  that  the  vestibule  is  especially  important  for  the  maintenance 
of  muscle-tonus  throughout  the  body.  The  cochlea  is  only  slightly  de- 
veloped in  fishes,  bu^  in  birds  it  reaches  a  fair  development.  Corresponding 
to  these  observations  the  majority  of  the  fibers  of  the  auditory  nerve  go  to 
the  labyrinth  and  saccule.  In  mammals,  for  the  first  time,  the  portion  of 
the  nerve  which  supplies  the  cochlea  becomes  large. 

In  the  brain  one  may  recognize  that  in  all  lower  vertebrates  the  major 
part  of  the  auditory  nerve  ends  in  a  striking  knob-like  nucleus,  which  is 
laterally  located  in  the  medulla  where  the  peduncles  of  the  cerebellum  come 
down.  Lodged  in  the  angle  between  the  medulla  and  cerebellum  and  as 
high  up  the  vertebrate  scale  as  to  the  birds,  always  covered  with  a  formation 
similar  to  the  cortex  of  the  cerebellum,  lies  this  great  nucleus  of  the  Acusti- 

(91) 


92 


ANATOMY   OF   THE    CENTBAL   NEKVOUS    SYSTEM. 


ens,  and  receives  on  its  ventral  side  the  fibres  of  the  auditory  nerve.  These 
fibers  divide  at  once  into  ascending  and  descending  branches  and  traverse 
the  ganglion  in  dense  fasciculi  before  they  divide  up  and  terminate.  These 
fibers  probably  all  arise  from  the  ganglion-cells  in  the  ear.  (Compare  Fig. 
16  [6],  Fig.  40  [Z>],  and  Fig.  47.). 

A  cross-section  through  the  lateral  part  of  the  medulla  in  the  region 
where  the  principal  nucleus  of  the  Acusticus  is  fully  developed  shows  that 
under  the  cortex  of  this  body  lie  very  many  sections  of  fibers.  The  nucleus 
has  developed  a  special  field,  which  has  been  designated  by  Ahlborn  as  the 
acusticus  field.  A  large  part  of  the  fibers  which  lie  here,  all  of  which  come 
from  the  Acusticus,  turn  upward  toward  the  cerebellum  and  end  in  another 
nucleus,  the  Nucleus  acustico-cerebellaris,  which  lies  antero-dorsally  adja- 


Tr.  acust.-tectalis  dors. 

Rud.  desc.  N.  acust.  Acusticus  field 

N.  facialis 


Tr.  cerebello-sp 


Fig.  49.— Most  posterior  portion  of  the  acusticus  nucleus  of  Alligator  luclus. 


cent  to  the  principal  nucleus  of  the  Acusticus.  Other  fibers  end  in  the 
principal  nucleus,  and  a  third  portion  proceeds  backward  as  a  posterior 
root.  • 

The  two  mentioned  acusticus  nuclei  are  connected  with  the  cerebellum 
through  numerous  fibers;  especially  with  two  spheroidal  nuclei,  which  lie 
close  to  the  roof  of  the  ventricle, — the  roof -nuclei  of  the  cerebellum, — where 
a  marked  decussation  takes  place.  But  several  cerebellar  fibers  pass  direct  to 
the  auditory  nerve  itself:  the  direct  sensory  cerebellar  tract. 

From  the  reptiles  upward  through  the  vertebrate  series  one  recognizes 
that,  besides  the  two  nuclei  mentioned,  new  ones  arise  which,  among  the 
fishes  and  amphibians,  are  present  in  only  a  rudimentary  form.  These 
nuclei  form  a  large  mass  located  quite  laterally  from  the  principal  nucleus, 


THE    MEDULLA.  93 

which  consists  essentially  of  large  cells.  One  can  easily  differentiate  them 
in  birds  and  mammals.  They  are  designated  in  the  latter  as  ventral  nucleus 
and  Tuberculum  acusticum,  and  are  here  larger  than  the  principal  nucleus. 
This  last  is  called  in  mammals  the  Nucleus  dorsalis.  This  homology,  how- 
ever, stands  on  very  weak  legs,  as  could  be  demonstrated  if  we  could  go 
more  into  the  details  of  the  acusticus  nuclei  of  individual  vertebrates. 

The  terminations  of  the  auditory  nerves  are  connected,  not  only  with 
the  cerebellum,  but  with  numerous  other  parts  of  the  brain.  The  whole 
lateral  region  of  the  medulla  occupied  by  the  auditory  nerves  is  traversed  by 
fibers  and  dotted  with  nuclei,  which,  either  directly  or  indirectly  through 
collaterals,  maintain  a  connection  with  the  Eighth.  For  mammals  the 
relations  are  approximately  known.  For  lower  vertebrates  the  following 
may  be  advanced: — 

On  the  median  side  there  uniformly  arise  (observed  in  Selachia, 
Teleostei,  Eeptilia,  and  Aves)  fibers  which  pass  inward  into  the  medulla  and 
connect  with  a  small  ganglion  there:  Oliva  superior.  In  mammals  this  body 
has  long  been  known  as  the  Corpus  trapezoides.  It  has  also  been  demon- 
strated that  we  have  to  deal  here  with  a  part  of  the  Tractus  acustico-tectalis 
(Fig.  49):  the  central  connection  with  the  roof  of  the  midbrain.  Doubtless 
there  exists  also  another  central  connection  in  the  lower  vertebrates  which 
does  not  take  its  way  through  the  Corpus  trapezoides.  This  is  much  the 
larger  tract  in  all  animals  below  the  mammals.  ISTote  in  Fig.  49  thick,  easily 
visible  fibers,  arising  from  the  principal  nucleus  in  a  strong  tract,  passing 
direct  to  the  median  line  of  the  fourth  ventricle  near  the  floor,  where  it 
approaches  the  fasciculus  longitudinalis  posterior  and  even  passes  through 
this  to  the  opposite  side.  It  probably  also  reaches  the  tegmentum  of  the 
midbrain.  Then  we  would  have  a  Tractus  acustico-tectalis  ventralis,  which 
passes  through  the  olivary  body  into  the  fillet,  and  also  a  Tractus  acustico- 
tectalis  dorsalis,  which  would  reach  the  same  destination  by  another  route 
(see  Figs.  48  and  49). 

Dorsal  to  the  principal  nucleus  of  the  Acusticus  lies  (in  all  vertebrates 
above  fishes),  imbedded  in  the  most  ventral  portion  of  the  cerebellum,  a 
large  nucleus  of  multipolar  ganglion-cells  which,  in  close  connection  with 
the  place  of  origin  of  the  "tonus  nerves,"  send  their  neuraxons  through  the 
territory  of  the  Acusticus  back  toward  the  spinal  cord.  This  nucleus  is 
known  in  mammals  as  Deiter's  nucleus,  in  general  as  Nucleus  tractus 
acustico-spinalis.  It  is  possibly  a  part  of  the  apparatus  which  is  necessary 
to  transmit  to  the  body-musculature  the  impressions  received  from  the 
labyrinth  (see  Fig.  47).  It  is  interesting  to  note  in  this  connection  that 
in  Teleostei  a  branch  from  the  region  leaves  the  brain,  not  with  the  Acusti- 
cus, but  (Stannius)  in  the  nervous  system  of  the  lateral  line  supplied,  for 
the  most  part,  by  vagus  branches,  with  which  they  become  associated.  The 


94  ANATOMY    OF   THE    CENTRAL   NERVOUS    SYSTEM. 

significance  of  the  lateral  line  and  its  associated  structures  as  an  organ  of 
equilibration  is  made  probable  through  this  anatomical  relation. 

When  you  are  reminded  (1)  that  in  the  acusticus  region  of  the  medulla 
the  long  fibers  of  Manther  arise, — fibers  which  end  only  in  the  posterior 
region  and  with  which,  in  the  spinal  cord,  we  became  acquainted  as  the 
Tractus  acustico-spinalis  (Figs.  29  and  40);  (2)  that  the  great  terminal  cells 
of  these  gigantic  fibers  ramify  the  acusticus  region  with  their  dendrites; 
then  it  will  be  clear  to  you  what  an  important  center  of  association  for  the 
most  diverse  regions  lies  in  the  middle  of  the  medulla  oblongata.  The 
physiological  experiments  and  the  considerations  which  are  involved  in  these 
anatomical  relations  lead  to  the  conclusion  that  the  part  of  the  medulla  just 


Fig.  50. — Section  of  the  medulla  of  Alligator  lucius  at  the  level  of  the 
motor  nucleus  of  the  Trigeminus.  Simply  the  contour  of  the  nerve  is  repre- 
sented. Compare  the  thin  Facialis  in  Fig.  49  with  the  large  motor  trunk  of 
the  Trigeminus  shown. 


described  represents  an  important  center  for  the  maintenance  of  general 
equilibrium. 

At  the  level  of  the  acusticus  nucleus  the  motor  columns,  which  reach 
toward  the  brain  from  the  spinal  cord,  are  not  yet  exhausted.  They  may  be 
best  imagined  as  a  thin  plate  which  bends  greatly  toward  the  sagittal  plane, 
although  somewhat  removed  from  it,  in  the  oblongata.  From  the  dorsal 
part  of  this  plate  near  the  spinal  cord  the  Hypoglossus  arose.  In  the  acusti- 
cus level  there  arises  the  Abducens:  a  part  of  the  plate  whose  course  may  be 
easily  recognized  on  Fig.  49.  The  ventral  portion  does  not  send  its  fibers 
out  direct,  but  collects  them  from  some  distance  into  little  fasciculi,  which 
then  all  turn  dorsally  in  order  to  bend  laterally  when  they  approach  the  gray 
matter  of  the  floor.  This  curious  knee-like  course  has  already  been  met  in 


THE    MEDULLA. 


95 


the  Accessorius  (Fig.  43):  a  nerve  which  left  the  same  cell-column  farther 
posterior;  also  a  part  of  the  motor  vagus  root  (Fig.  46)  presents  a  similar 
thing.  We  now  come  to  the  two  nerves  which  arise  from  the  major  part  of 
the  cell-column  under  consideration:  viz.,  the  Facialis  and  the  motor 
Trigeminus.  Both  are  not  always  sharply  differentiated  from  each  other  in 
the  region  of^the  roots.  In  the  lower  vertebrates  the  motor  Facialis  is 
usually  much  smaller  than  the  masseteric  branch  of  the  Trigeminus,  prob- 
ably because  the  face-musculature  is  less  developed.  Fig.  49  shows  the  posi- 
tion of  the  Facialis  and  of  the  nucleus  of  the  Abducens  in  the  alligator  and 
in  Fig.  50  is  presented  a  section  which  cuts  the  motor  column  at  a  higher 
level  when  it  dilates  in  the  dorsal  portion  for  the  nucleus  of  the  Trigeminus. 
The  nucleus  of  the  Facialis  is  not  a  single  structure.  In  the  longitudinal 
as  well  as  in  the  antero-posterior  direction  it  shows  interruptions.  For 


Fig.  51. — Lacerta  agilis.    Region  of  exit  of  the  Trigeminus  (N.V.). 


that  reason  one  might  easily  designate  in  different  animals  different  cell- 
groups  as  the  origin  of  the  nerve.  But  all  of  these  cell-groups  belong  to  the 
same  mass  of  great  multipolar  cells,  whose  neuraxons  pass  into  motor  nerves. 
At  the  anterior  end  of  the  medulla  the  gray  mass  which  received  the 
sensory  nerves  on  the  latero-dorsal  aspect  becomes  again  very  much  en- 
larged. At  this  point  the  Trigeminus  nerve  enters  it.  In  this  frontal 
sensory  nucleus  of  this  nerve  only  a  part  of  the  fibers  from  the  Gasseriau 
Ganglion  end,  while  a  greater  part  turn  toward  the  spinal  cord,  there  to 
gradually  enter  the  gray  matter,  which  we  see  in  all  sections  from  the  upper 
end  of  the  spinal  cord  to  the  entrance  of  the  Trigeminus  into  the  medulla. 
This  descending  portion  has  been  described  as  the  bulbo-spinal  root  of  the 
Trigeminus.  In  such  aquatic  animals  as  fishes,  dipnoi,  and  larval  amphibia 
there  exists  over  the  whole  head  a  system  of  canals  bearing  a  sensory  epithe- 
lium: an  apparatus  which  probably  serves  for  the  detection  of  changes  of 


96 


ANATOMY    OF    THE    CENTRAL    NEEVOUS    SYSTEM. 


pressure  in  the  surrounding  medium.    It  at  least  appears  to  be  well  adapted 
to  such  a  purpose.    In  amphibia  it  disappears  when  terrestrial  life  is  entered 


Tr.  acust.  tect.^ 
pez.,  et  oliv.  sup.'  j 


Lobus  N.  trigemini 


Lobus  N.  vagi 


Tr.  vago-cerebellaris  et  tecta 

Nucl.  mot.  N.  vagi 
Radices  N.  vagi 

Fasc.  longit.  post,  et  Tr.  tecto-spinalis 
Bad.  mot.  N.  vagi 

Vagus  desc.  et  Tr.  vago-cerebellaris 
Tr.  bulbo-spinalis  N.  trig. 

Tr.  assoc.  breves  et  fibr.  arcif.  ext. 


Lobus  N.  trigemi 


Radices  lobaresl 
N.trig.j 


tion  of  the  acnsticns 
region,  with  descend- 
ing acusticus  roots 


- .'.,:,i.--l_ Decussatio  (acust.?) 


Divertic.  ventr.  quart. 
—  /  Tractus  quinto-  cerebel- 

pFsc.  long.  post. 
!-Tr.  assoc.  breves 

-Tr.  bulbo-spinalis  N.  trig. 
•Tr.  vago-cerebellaris 


Figs.  52  and  53.— From  the  Medulla  of  the  barbel,  Barbus  fluviatilis  ; 
vagus  and  trigeminus  roots. 


upon.    On  the  innervation  of  this  apparatus,  as  well  as  on  the  sensory  nerves 
of  the  head  in  general,  we  have  been  enlightened  only  in  recent  years 


THE    MEDULLA. 


97 


through  studies  of  f 'incus,  of  Cole,  and  especially  of  Oliver  S.  Strong.  It 
has  been  demonstrated  that  all  of  these  animals  possess  a  sensory  portion  of 
the  Nervus  facialis  which  innervates  this  canal-system  of  the  head.  Similar 
apparatus  on  the  trunk  receive  principally  branches  from  the  Vagus.  From 
what  part  of  the  brain  the  sensory  portion  of  the  Facialis  arises  is  uncertain. 
Further  investigation  is  necessary.  Strong  maintains  that  the  Tuberculum 
acusticum  comes  into  consideration.  To  the  author  it  seems  more  probable 
that  we  have  to  do  here  with  parts  which  have  been  previously  attributed 
to  the  terminal  apparatus  of  the  Trigeminus.  In  all  teleosts  there  is,  in  con- 
nection with  the  terminal  nucleus  of  the  Trigeminus,  a  large  lobe  which,  in 
cyprinoids  and  other  fishes,  is  connected  with  that  of  the  opposite  side,  and 
is  located  transversely  over  the  ventricle.  Powerful  bundles  of  fibres — desig- 


Acust.  desc._— . 

Nucl.ventr.l 

N.acustJ. 


Fig.  54. — From  the  medulla  of  Barbus  fluviatilis ;    Vagus  and  Trigeminus  roots. 


nated  in  the  figures  as  "Had.  lobares  N.  trigem." — pass  out  of  the  Lobus 
trigemini.  Should  further  investigation  substantiate  the  author's  supposi- 
tion that  we  are  dealing  here  with  the  terminal  nucleus  of  the  sensory  Faci- 
alis, then  the  names  in  the  Lobus  Nervi  facialis  will  have  to  be  changed. 
What  is  designated  (Fig.  54)  as  Tractus  Nervi  trigemini  ex  lobo  probably 
represents  the  sensory  Facialis.  But,  without  doubt,  the  origin  of  the 
nucleus  requires,  in  lower  vertebrates,  to  be  most  carefully  studied  anew. 

Figs.  52,  53,  and  54  will  elucidate  the  point  better  than  a  description. 

In  birds  and,  especially,  in  the  armored  reptiles  the  frontal  nucleus 
of  the  Trigeminus  is  much  less  developed  than  in  other  animals.  With  each 
Nervus  trigeminus  there  passes  a  fasciculus  from  the  brain,  which  origi- 
nates from  the  roof  of  the  midbrain.  This  Radix  mesencephalica  trigemini 
arises  from  large,  pear-shaped  cells,  which  lie  near  the  aqueduct  in  mammals. 


98  ANATOMY    OF   THE    CENTRAL    XERVOUS    SYSTEM. 

It  is  probable  that  this  nucleus  is  identical  with  one  consisting  of  exactly- 
similar  cells,  which  one  finds  in  amphibians  and  reptiles  quite  near  the 
median  line  of  the  Tectum  opticum,  or  roof-nucleus,  of  the  midbrain,  which 
is  especially  large  in  turtles. 

All  trigeminus  nuclei  receive  important  afferent  bundles  from  the  fillet. 
These  approach  the  nuclei  after  decussation,  as  is  the  case  with  other  nerve- 
nuclei.  Besides  this  they  receive  from  the  cerebellum  a  contribution  regard- 
ing which  it  is  uncertain  whether  it  ends  in  the  nucleus  or  leaves  the  brain 
direct  with  the  nerve.  This  accretion  from  the  cerebellum  to  the  lobus 
trigemini  is  very  large. 

Up  to  the  present  we  have,  for  the  sake  of  clearness,  let  it  be  understood 
that  the  medulla  contains  nothing  but  the  nuclei  of  the  cranial  nerves,  with 
their  associated  tracts  and  connections.  But  there  are  still  other  fibers  which 
enter  the  medulla  on  their  way  from  the  spinal  cord  to  the  cerebellum,  as 
well  as  some  which  pass  from  the  cerebellum  into  the  nuclei  of  the  medulla 
itself.  Moreover,  the  medulla  contains,  besides  the  cells  and  fibers  of  the 
association-system,  a  number  of  special  ganglia.  Only  one  of  these — the 
Oliva  superior — has  been  mentioned  in  connection  with  the  description  of 
the  Acusticus.  But  in  all  vertebrates  there  are  still  other  groups  of  nuclei. 
In  mammals  the  largest  of  these  is  the  group  designated  Oliva  inferior, 
which  stands  in  close  relation  to  the  cerebellum,  by  which  fact  it  is  char- 
acterized. Up  to  the  present  time  (if  one  stands  by  this  characteristic)  an 
oliva  inferior  has  not  been  discovered  in  any  vertebrate  except  in  the  mam- 
mal. We  may,  indeed,  find,  in  reptiles,  birds,  and  even  in  amphibians,  nuclei 
which  are  similarly  located  in  the  medulla  and  which,  in  reptiles,  are  of  simi- 
lar structure  (see  Fig.  46);  but  a  positive  interpretation  of  this  group  is,  as 
yet,  lacking.  The  same  is  true  of  nuclei  which  are  everywhere  demonstrable 
at  the  ventral  margin  of  the  medulla,  and  especially  toward  the  posterior 
end.  At  this  point  one  finds,  in  mammals,  the  nuclei  arciformes.  Of  all  the 
details  given,  or  possible  still  to  give,  remember  especially  that  the  numer- 
ous longitudinal  bundles  whose  cross-sections  one  sees  in  the  ventral  and 
lateral  regions  of  all  cross-sections  of  the  medulla  contain,  besides  the  fasciculi 
of  the  association-system,  connecting-fibers  to  the  mesencephalon  and  thala- 
mencephalon.  We  have  already  met  the  tracts  from  the  thalamencephalon 
to  the  spinal  cord  when  considering  the  lateral  columns.  Even  in  the 
medulla  this  tract,  especially  well-marked  in  fishes,  lies  in  the  lateral  region. 
It  is  much  larger  than  in  the  spinal  cord  and  gradually  decreases  posteriorly. 

There  are  two  fiber-systems  of  the  medulla  which  we  must  now  con- 
sider somewhat  in  detail,  because  they  are  of  especial  importance  physio- 
logically. 

The  first  one  of  these  is  the  fascicle  from  the  nuclei  of  the  posterior 
columns  to  the  fillet,  the  most  anterior  fasciculi  of  the  Tractus  tecto-i 


THE    MEDULLA.  99 

They  have  already  been  presented  as  Fibrce  arcuatce  internee  (Figs.  42  and 
43).  This  tract,  which  reaches  full  development  only  in  the  mammals, 
is  probably  already  present  among  fishes.  It  is  a  portion  of  the  great  central 
fiber-system  from  the  sensory  terminal  nuclei.  After  decussation  it  passes 
toward  the  brain  in  the  fillet,  and  with  it  are  gradually  associated  all  of  the 
crossed  bundles  from  the  nuclei  of  the  cranial  nerves, — the  Tractus  tecto- 
nucleares, — together  forming  the  fillet. 

The  second  important  fiber-system  belongs  to  the  lateral  margin  of  the 
medulla.  Here  lies  the  Tractus  cerebello-spinalis,  ventral  from  the  spinal 
root  of  the  Trigeminus.  It  arises,  also,  from  the  termini  of  the  sensory 
nerves  in  the  spinal  cord.  It  does  not  turn  toward  the  fillet,  however,  but 
passes  anteriorly  to  the  exit  of  the  Acusticus,  where  it  turns  dorsally  to  the 
cerebellum.  On  the  way  it  has  received  reinforcements  from  the  posterior 
columns, — the  Fibrce  arcuatce  externce, — demonstrated  in  fishes,  amphibians, 
and  birds.  The  united  bundle  is  called  the  Corpus  restiforme:  inferior 
peduncle  of  the  cerebellum.  It  has  been  carefully  studied  only  in  mammals; 
in  this  class  it  contains  still  other  elements.  Only  a  few  of  them  are  found 
also  in  birds  and  reptiles:  e.g.,  the  acusticus-cerebellar  tract  and  the  bundle 
from  the  Deiter  nucleus  to  the  spinal  cord. 

Where  an  olivary  body  is  demonstrable  the  fibers  run  from  it  to  the 
cerebellum  through  the  inferior  peduncle  restiforme. 

At  the  frontal  end  of  the  medulla  the  Tractus  tecto-bulbares  et  spinales 
turns  dorsally  to  reach  the  roof  of  the  midbrain.  At  this  point  a  nucleus 
is  always  located  within  it  (Fig.  50), — the  tegmental  nucleus, — which  is 
much  subdivided.  The  tracts  to  the  cerebellum  have,  at  this  point,  already 
turned  upward;  those  which  pass  to  and  from  the  cranial  nerves  are  present 
only  in  small  measure.  What  remains  of  the  features  mentioned  is  confined 
to  tracts  which  pass  downward  from  the  cerebellum  and  then  to  tracts  which 
pass  toward  the  medulla  from  the  mesencephalon  and  the  thalamencephalon. 
They  lie  in  the  ventral  divisions,  and  are  not  yet,  with  certainty,  to  be  differ- 
entiated from  the  fillet  in  the  lower  vertebrates.  Besides  this,  the  Fascic- 
ulus longitudinalis  posterior  lies  dorsally  and  distributed  over  the  whole 
breadth  of  the  lateral  areas, — the  system  of  commissure  cells  with  short 
bundles  joining  the  different  levels  of  the  medulla  with  the  floor  of  the  mid- 
brain. 

In  mammals — but,  so  far  as  I  know,  only  in  these — still  another  tract 
descends  from  the  cerebrum,  which  remains  in  part  in  the  frontal  ganglia 
to  be  described  later  and  in  part  ends  in  the  nuclei  of  the  cranial  nerves 
with  their  final  processes  even  in  the  spinal  cord,  where  we  have  already 
learned  to  know  it  as  Tractus  cortico-spinalis. 

We  may  now  close  our  survey  of  the  structure  of  the  Medulla  Ob- 
longata.  Now  that  it  is  shown  what  important  nuclei  of  origin  and  termina- 


100  ANATOMY    OF   THE    CENTRAL   NERVOUS    SYSTEM. 

tion  lie  here;  what  great  association-systems  occupy  the  whole,  connecting 
all  of  its  levels  among  themselves  and  with  higher  and  lower  centers;  what 
important  connections  run  from  the  oblongata  to  other  parts  of  the  brain, 
it  becomes  evident  that  just  this  part  of  the  brain  is  the  most  important  for 
the  maintenance  of  life.  On  the  one  hand,  one  may,  in  a  lower  vertebrate, 
remove  everything  anterior  to  the  medulla  without  so  disturbing  the  vital 
functions  that  death  supervenes,  and  may,  on  the  other  hand,  remove  the 
whole  spinal  cord  without  inducing  anything  more  than  complete  motor 
and  sensory  paralysis.  But  no  vertebrate  can  survive  the  removal  of  the 
Medulla  Oblongata,  that  general  origin  for  the  most  important  nerves,  that 
great  center  of  co-ordination. 

The  importance  of  the  Medulla  Oblongata  for  the  existence  of  the 
animal  corresponds  to  the  fact  that  this  part  of  the  brain  reaches  a  high 
development  earlier  than  any  other  part.  This  is  true,  both  in  the  phy- 
logeny  and  in  the  ontogeny  of  the  central  nervous  system. 


CHAPTEE    VIII. 
THE  CEEEBELLUM. 

DORSAL  to  the  Medulla  Oblongata  and  connected  with  it  through 
several  tracts,  lies  the  Cerebellum.  It  is  continuous  posteriorly  with  the 
Plexus  chorioidei  ventriculi  quarti  and  anteriorly  with  a  thin  sheet, — the 
Velum  anticum, — which  passes  to  the  roof  of  the  mesencephalon. 

A  study  of  Fig.  55  will  make  it  evident  that  no  part  of  the  brain, — the 
cerebrum  probably  excepted, — manifests  so  many  variations  in  its  degree  of 
development  as  does  the  cerebellum.  The  cerebellum  is  not  more  highly 
developed  in  the  higher  animals  than  in  the  lower,  as  is  the  case,  however, 
with  the  cerebrum.  On  the  other  hand,  we  meet,  even  between  closely 
related  animals,  very  striking  differences.  The  simplest  form  in  which  we 
find  the  cerebellum  is  presented  by  the  Cyclostomes  and  Amphibia.  That 
portion  of  the  cerebellar  roof  which  is  turned  toward  the  midbrain  is 
thickened  into  a  narrow  plate  or  ridge,  which  lies  transverse  to  the 
anterior  end  of  the  fourth  ventricle.  Even  the  reptiles  do  not  possess 
a  cerebellum  which  is  essentially  higher  than  this,  except  that  those  rep- 
tiles which  swim  (alligators,  crocodiles,  etc.)  possess  a  cerebellum  of 
twice  the  relative  size  and  extent.  Those  great  swimmers — the  teleostei 
and  the  selachia — possess  a  cerebellum  which  is  so  enormously  developed 
that  it  must  lie  in  large  transverse  folds  (Fig.  55,  A);  indeed,  in  the 
teleosts  the  cerebellum  pushes  forward  under  the  roof  of  the  midbrain 
into  the  aqueduct  (Fig.  55,  (7).  But  that  sluggish  mud-fish, — the  Dipnoi, — 
which,  on  the  basis  of  other  structures  has  been  accorded  the  highest  place 
among  the  fishes,  has  a  small  cerebellum. 

A  glance  at  Fig.  55  shows  that,  through  the  dorsal  evagination  of  the 
cerebellar  plate,  there  is  produced  a  continuation  into  the  cerebellum  of  the 
fourth  ventricle.  This  Ventriculus  cerebelli  is  still  demonstrable  when  the 
size  of  the  cerebellum  has  greatly  increased,  as  in  birds  and  mammals,  ex- 
cept that  it  is  then  very  narrow,  and  in  the  peripheral  portions  the  narrow 
clefts  usually  completely  disappear. 

Into  the  cerebellum  of  fishes,  amphibians,  and  reptiles  there  pass  tracts, 
not  only  from  the  spinal  cord,  but  also  from  the  thalamencephalon  and 
mesencephalon.  The  same  tracts  are  found  also  in  birds  and  mammals. 
But  in  the  latter  very  large  tracts  pass  also  from  the  cerebrum  to  the  cere- 
bellum. These  last-named  tracts  pass  into  new  and  special  structures,  which 

(101) 


102 


ANATOMY    OF    THE    CENTRAL    NERVOUS    SYSTEM. 


appear  on  either  side  of  the  median  portion, — the  Hemisphceria  cerebelli.  In 
mammals  they  are  developed  synchronously  with  the  appearance  of  the 
Pons  to  proportions  which  greatly  exceed  those  of  the  middle  part, — which 
latter  is  now  called  the  Vermis.  But  the  median  segment  of  the  cerebellum 
retains  even  in  man  the  characteristic  worm-like  transverse  folding  acquired 
by  the  cerebellar  plate  in  the  selachians.  Immediately  posterior  to  the 
cerebellum  we  meet  in  the  roof  of  the  medulla  ganglionic  masses  which 
send  out  fibers  of  the  Trigeminus  and  Acusticus.  Usually  fused  with  the 
cerebellum  these  form,  in  the  higher  vertebrates,  unimportant  nuclei;  in 
fishes,  however,  well-marked  lobes  (see  Fig.  55  A  and  (7). 

Nowhere  else  in  the  animal  kingdom  does  the  Vermis  cerebelli  reach 


Fig.  55. — Semidiagrammatic  sagittal  sections  through  the  vertebrate  brain. 
The  cerebellum  appears  in  black,  to  show  its  relative  size.  A,  Brain  of  Ray; 
B,  of  an  Amphibian;  C,  of  a  Trout-embryo;  D,  of  a  Bird. 


such  enormous  development  as  in  the  great  swimmers  and  the  birds.  This 
circumstance,  together  with  the  fact  that  in  the  same  animals  there  are 
especially  large  connections  with  the  tonus  nerves  of  the  labyrinth  and  with 
the  Trigeminus,  makes  it  most  probable  that  in  some  way  or  other  the  cere- 
bellum must  be  involved  in  the  maintenance  of  equilibrium.  This  is,  in 
fact,  indicated  in  its  general  development.  The  results  of  physiological  ex- 
periments indicate  the  same  thing. 

Phylogenetically  the  cerebellum  is  one  of  the  oldest  portions  of  the 
brain.  Experiments  upon  the  supra-oasophageal  ganglion  in  arthropoda 
indicate  that  it  fulfills  functions  equivalent  or  similar  to  those  of  the  cere- 
bellum in  higher  animals. 


THE    CEEEBELLUM. 


103 


The  cerebellum  is,  without  doubt,  then,  one  of  the  most  important 
parts  of  the  brain,  for  a  study  of  which  one  is  well  repaid. 

Its  structure  is  remarkably  simple,  and  similar  in  all  animals,  the  whole 
organ  being  a  repetition  of  a  simple  histological  type. 

As  previously  shown,  the  cerebellum  is  ontogenetically  developed  from 
a  simple  cell-plate;  and  the  figures  just  presented  make  it  evident  that  the 
same  is  true  of  its  phylogenetic  development.  All  of  the  manifold  forms 
of  the  cerebellum  arise  through  a  folding  of  the  primitive  cerebellar  plate, 
the  object  of  the  folding  being  evidently  an  increase  of  surface.  Whether 


Fig.  56. — Sagittal  section  through  the  cerebellum  of  the  lizard,  Yaranus 
griseus,  showing  the  external  lamina  (fac.  front.)  and  the  internal  lamina 
(fac.  caud.). 


the  plate  extends  upward  or  downward,  whether  it  remains  small  or  pro- 
gresses to  a  high  development,  it  is  always  built  on  the  same  type.  Let  us 
take,  as  our  starting-point,  the  further  study  of  the  reptilian  cerebellum, 
because  it  is  a  simple  thin  plate  which,  lying  transverse  to  the  ventricle  and 
transverse  to  the  long  axis  of  the  brain,  extends  toward  the  crown.  One 
may  differentiate  a  frontal  face,  turned  toward  the  midbrain,  and  a  pos- 
terior face.  A  section  shows  at  once  that  these  two  lamina?  have  a  different 
structure.  The  posterior  (internal)  one  is  rich  in  ganglion-cells,  while  the 


104  ANATOMY   OF   THE    CENTRAL   NERVOUS    SYSTEM. 

anterior  (external)  lodges  principally  the  dendrites  from  the  posterior 
lamina. 

Just  at  the  boundary  of  the  two  lamina  lies  a  layer  of  large  cells  extra- 
ordinarily similar  in  all  vertebrates,— the  layer  of  Cells  of  Purkinje,  and 
partly  in  the  posterior  or  internal  cerebellar  lamina  (granular  layer). 

The  small  multipolar  ganglion-cells  which  fill  the  internal  lamina 
seem  all  to  send  up  their  neuraxons  into  the  molecular  or  external  lamina. 

There  are,  however,  in  this  layer,  and  close  to  the  cells  of  Purkinje, 
several  other  types  of  cells  which,  though  known  in  birds  and  fishes,  have 
been  closely  studied  in  mammals,  and  will,  therefore,  be  described  later. 

The  mass  of  fibers  which  pass  into  the  cerebellum  in  amphibians  and 
reptiles  is  so  small  that  they  scarcely  make  a  separate  layer  on  the  epithelium 
of  the  ventricle,  but  break  up  at  once  and  pass  into  the  fine  net-work  of  the 
latter.  In  teleosts,  selachians,  and  higher  vertebrates  the  condition  is  differ- 


c 

Fig.  57. — Somewhat  diagrammatic  sagittal  sections  through:  (A)  Cerebel- 
lum of  a  lizard;  (B)  Type  of  cerebellum  of  an  alligator,  crocodile,  or  turtle;  (G) 
Type  of  cerebellum  of  a  bird  or  mammal.  To  illustrate  the  increase  of  the  cere- 
bellum through  folding  of  the  cerebellar  plate  in  the  direction  of  the  arrow 
over  A.  ' 


ent.  Here  such  a  mass  of  medullated  fibers  pass  into  the  cerebellum  that 
one  may  always  observe,  between  the  epithelium  of  the  ventricle  and  the 
internal  or  posterior  lamina,  a  separate  and  sometimes  very  important  layer 
composed  solely  of  these  afferent  fibers.  This  is  the  medullary  layer,  or 
center  of  the  cerebellum.  The  figure  of  Varanus  (Fig.  56)  shows  the 
medullary  center  only  in  traces.  Into  this  layer  pass  tracts  from  the  mid- 
brain  and  the  thalamus,  which  are  highly  developed  in  fishes,  but  which 
are  also  demonstrable  in  other  animals.  For  the  lower  vertebrates  the 
material  is,  at  present,  insufficient.  What  is  known,  however  (Teleosts, 
Schaper;  Birds,  E.  y  Cajal,  Kolliker,  and  Edinger),  shows  that  even  in 
the  more  detailed  relations  the  lower  vertebrates  are  similar  to  the  mammals. 
It  may  be  thus  briefly  summarized:  In  the  cerebellum  fibers  end  and 


THE    CEREBELLUM.  105 

fibers  begin;  and  through  the  branches  of  the  cells  located  there  is  furnished 
a  wide  range  of  possibilities  in  the  co-ordination  of  the  processes  which  go 
on  there. 

From  the  simple  type — that  of  Varanus,  for  example — we  may  readily 
derive  most  of  the  other  types  of  cerebellum.  We  have  to  deal  with  only 
two  factors:  with  the  development  of  the  cortex  and  of  the  medullary 
center.  If  the  cortex  increases  in  size  it  presents  folds.  Fig.  57  shows  how 
the  simple  lizard  type  is  doubled  in  the  swimming  alligator  and  turtle, 
and  how,  through  a  farther  folding  of  the  same  cerebellar  plate,  the  avian  or 
mammalian  type  may  be  derived.  In  teleosts  the  surface  is  relatively  greater 
than  in  amphibians  and  reptiles  and  it  arises  from  the  facts  (1)  that  the 
molecular,  or  inner,  layer  is  thicker;  and  (2)  that  an  unusual  number  of 
afferent  bundles  pass  into  the  cerebellum,  much  increasing  the  medullary 
center  over  the  ventricle.  Thus  arises  an  apparently  massive  body  (see 


Fig.  58. — Sagittal  section  a  little  to  one  side  of  the  median  line 
through  the  cerebellum  of  a  small  ray. 


Fig.  44),  in  which  the  part  that  lies  under  the  roof  of  the  midbrain  is 
designated  the  Valvula  cerebelli.  It  has  already  been  mentioned  above  that 
at  the  posterior  end  of  the  cerebellum  there  are  associated  parts  which  stand 
in  special  relation  to  the  nuclei  of  the  Acusiicus  and  the  Trigeminus.  The 
separation  of  this  region  from  the  cerebellum  is  not  yet  to  be  sharply  made 
in  most  vertebrates,  but  in  selachians  they  are  separately  marked  trans- 
verse folds;  so  that  one  may  speak  of  a  Lobus  cerebellaris  Acustici  and  a 
Lobus  cerebellaris  Trigemini  (see  Fig.  58). 

In  teleosts  and  even  in  selachians  the  cerebellum  cortex  extends  some 
distance  posteriorly  and  beyond  these  accessory  structures.  In  birds  and 
mammals  they  are  completely  included  in  the  formation  of  the  cerebellum, 
where  they  lie  in  the  median  portion, — in  the  Vermis. 

Certain  cell-groups  easily  demonstrable  in  mammals  and  birds,  as  yet 
hardly  known  in  reptiles  and  amphibians,  and  easily  found — to  the  extent 
of  one  cell-group — in  fishes,  may  be  called  the  special  cerebellar  nuclei.  The 


106 


ANATOMY    OF   THE    CENTRAL    NERVOUS    SYSTEM. 


last-named  cell-group  consists  of  two  large  spherical  nuclei  lying  rather  far 
to  the  posterior  aspect, — the  nuclei  globosi  cerebelli  (see  Fig.  47).  They 
lie  so  direct  in  the  plane  of  the  nucleo-cerebellar  tract  and  are  so  completely 
surrounded  by  the  bundles  of  this  tract,  that  they  are  probably  to  be 
counted  in  with  this  tract.  In  birds,  and  probably  also  in  reptiles,  small 
masses  of  cells  lie  laterally  from  these:  the  Nuclei  laterales  Vermis.  In 
mammals  one  finds  in  the  same  region  not  only  several  small  nuclei,  but 
quite  lateral  from  this,  in  the  cerebellar  hemispheres,  a  large  much-folded 


Fig.  59. — Frontal  section  through  the  midbrain  of  a  shark:  Scyllium  cani- 
cula.  Length  of  body,  thirty  centimeters.  Showing  the  decussation  of  the 
Tractus  tegmento-cerebellares. 


nucleus:  the  Oliva  cerebelli  or  the  Nucleus  dentatus  (Nuc.  dentatus  Olivce). 
It  occupies  the  superior  peduncle  of  the  cerebellum.  It  has  not  yet  been 
recognized  in  the  lower  vertebrates,  but  it  is  probable  that  it  exists,  because 
in  these  animals  the  superior  peduncle  enters  the  cerebellum. 

Of  the  connections  and  the  definite  course  of  the  fibers  of  the  cerebellum 
there  is,  as  yet,  little  known. 

To  be  sure,  we  possess  minute  descriptions  for  several  different  verte- 


THE    CEREBELLUM. 


107 


brate  classes;  but  sufficient  work  has  not  yet  been  done  with  developmental 
or  degeneration  methods.  Accept  what  is  here  presented  as  simply  that 
which  may  be  with  some  certainty  now  expressed. 

The  cerebellum  stands  in  connection  with  other  parts  of  the  brain 
through  its  peduncles.  The  fiber  constituents  of  the  peduncles  are,  for  the 
most  part,  constant,  except  that  in  the  lower  vertebrates  appear  certain 
tracts  not  yet  found  in  mammals  and  birds,  while  in  mammals  there  is  a 
cerebsal  connection  which  is  peculiar  to  this  class. 

Least  known  as  to  their  real  origin  are  several  frontal  tracts.  In 
teleosts,  whose  large  cerebellum  contains  easily  recognizable  afferent  tracts, 
two  tracts  pass  from  the  thalamencephalon:  a  fine-fibered  posterior  one  and 


Deenss.  valvuia 


Tr.  tegmento-cerebellaris 

f  Molecular  Inyer  and  cells  ol 
\     Purkinje 


Pars  dorsal.  Ganglii  Istlimi 

Granular  layer 

Tr.  cerebello-spinalis 


Fig.  60. — Section  through  the  velum  and  cerebellum  of  a  large 
lizard:    Lacerto  muralis. 


a  coarse-fibered  frontal  one,  the  first  into  the  cerebellum  and  the  second  into 
the  Valvuia  cerebelli,  the  portion  which  lies  under  the  roof  of  the  mid- 
brain.  These  are  called  Tractus  thalamencephalo-cerebellares.  These  bundles 
have  not,  with  certainty,  been  found  in  other  animals.  The  Brachium  con- 
junctivum  anterius  or  superior  cerebellar  peduncle,  is  always  present  as 
the  Tractus  tegmento-cerebellaris.  This  is  a  bundle  from  a  ganglion,  which 
lies  at  the  posterior  end  of  the  base  of  the  thalamencephalon.  Not  far  from 
its  origin  it  decussates  with  its  fellow.  This  decussation,  which  always  lies 
at  the  level  of  the  Oculo-motorius  near  the  base,  is  a  good  point  of  orienta- 
tion in  investigations  in  brain-anatomy.  Thence  the  fibers  pass  dorsally 
into  the  cerebellum  (see  Figs.  59,  61,  71,  83,  84,  and  85). 

Besides  the  tract  named,  still  other  fairly  large  bundles  enter  the 


108  ANATOMY   OF   THE    CENTRAL    NERVOUS    SYSTEM. 

anterior  end  of  the  cerebellum  in  fishes,  amphibians  and  reptiles,  but  decus- 
sate just  before  sinking  into  the  substance  of  the  cerebellum.  This  decussa- 
tion  does  not  lie  ventrally,  as  that  just  described,  but  dorsally  in  the  velum, 
just  posterior  to  the  decussation  of  the  Trochlearis,  easily  visible  in  reptiles 
(see  Fig.  60). 

The  fibers  of  this  Decussatio  veli  arise,  in  part,  from  the  midbrain,  but 
in  larger  part  from  the  trigeminus  nucleus.  The  detailed  relations  of  this 
Decussatio  veli  are  yet  to  be  determined. 

The  connection  between  the  cerebellum  and  the  spinal  cord  is  extra- 
ordinarily similar  in  all  vertebrates,  and  is  accomplished  through  the 
inferior  peduncles  of  the  cerebellum.  Here  one  always  meets  that  tract  from 
the  lateral  columns,  which,  arising  from  a  terminal  nucleus  of  the  sensory 
roots,  is  known  to  you  as  the  Tractus  cerebello-spinalis.  Associated  with  it 
is  the  bundle  from  the  Nucleus  of  Deiter  in  the  acusticus  region,  which 
bundle  probably  also  ends  in  the  lateral  columns.  At  any  rate,  Monakow 
could  observe  in  mammals,  and  Bandis  in  birds,  a  descending  degeneration 
from  this  nucleus  when  they  severed  an  inferior  cerebellar  peduncle.  The 
fibers  of  the  Tractus  cerebello-spinalis  probably  end  in  crossed  and  uncrossed 
ramifications  in  the  dorsal  plane  of  the  cerebellum  without  the  molecular 
or  inner  lamina. 

In  teleosts,  selachians,  reptiles,  and  birds  the  author  has  observed  that 
within  the  medulla  there  are  associated  with  the  mentioned  tracts  still 
other  afferent  tracts  from  the  nuclei  of  the  posterior  columns  and  from  the 
posterior  columns  direct.  The  latter  pass  around  the  medulla  ventrally, 
near  its  periphery, — Fibrse  arcuatag  externas, — till  the  tract  is  reached,  when 
they  fuse  with  it.  In  mammals  the  relations  are  the  same;  but  here  the 
inferior  cerebellar  peduncle  contains  yet  other  connections,  especially  the 
large  afferent  tract  to  the  Oliva, — Tractus  cerebello-olivaris,  which  has  not 
yet  been  found  in  other  classes. 

Where  the  inferior  cerebellar  peduncle  enters  the  cerebellum  is  the 
least  understood  portion  of  the  whole  nervous  system.  Here  lies  the  acusti- 
cus nucleus  and  several  nuclear  groups  whose  significance  is,  as  yet,  com- 
pletely problematical.  These  all  lie  mesially  from  the  peduncles.  But 
just  at  this  place  there  pass  into  the  medulla  the  Tractus  vago-  et  quinto- 
cerebellares  and  from  the  medulla  afferent  bundles  to  the  apparatus  of 
equilibrium,  which  may  pass  into  the  Nervus  vestibularis  and  into  the  Oliva 
superior.  The  middle  peduncle  reaches  a  considerable  size  only  in  the  mam- 
mals, where  it  carries  large  bundles  of  fibers  from  the  ganglia  of  the  pons 
up  into  the  cerebellum.  The  termini  of  these  fibers — the  cortex  of  the 
cerebellar  hemisphere — are  completely  lacking  in  other  animals,  in  which 
only  the  midportion — the  Vermis — develops.  One  set  of  fibers  which  lies 
in  the  middle  peduncle  is  also  demonstrable  in  lower  vertebrates.  That  is 


THE    CEREBELLUM. 


109 


a  fasciculus  which  passes  ventrally  from  the  cerebellum,  curves  around  the 
medulla  ventrally  for  a  short  distance,  just  to  where  it  reaches  the  median 
line,  where  it  bends  upward,  ascends  within  the  raphe,  finally  decussates, 
and  is  lost  in  the  lateral  portions  of  the  medulla, — the  Tractus  cerebello- 
tegmentalis. 

The  relation  of  the  arms  within  the  cerebellum  of  the  lower  vertebrates 
requires  elucidation.  There  is  an  open  field  here  for  the  degeneration- 
method.  Not  the  least  of  the  difficulties  in  the  study  of  the  intact  organ  is 
the  fact  that  several  tracts  cross  in  the  cerebellum  and  pass  to  little  known 
gray  masses.  In  teleosts  whose  large  cerebellum  is  quite  free  from  the  tracts 
from  the  cerebrum  more  is  known  with  certainty  than  is  the  case  in  the 
other  vertebrates.  Particularly  so  among  the  decussation-fibers,  the  largest 
are  those  which  belong  to  the  Tractus  nucleo-cerebellares  of  the  Vagus  and 


Fig.  61. — Sagittal  section  far  to  one  side  of  the  median  plane  through  the 
brain  of  an  eight-day  chick.  Only  a  part  of  the  fibers  are  medullated.  Showing 
the  origin  and  course  of  the  superior  and  inferior  cerebellar  peduncles. 

the  Trigeminus,  as  well  as  fibers  from  the  terminal  region  of  the  Acusticus. 
A  large  part  of  this  decussation  lies  on  the  ventral  side  of  the  cerebellum 
(Fig.  60)  close  above  the  roof  of  the  ventricle.  There  one  finds  in  teleosts  a 
good  point  of  orientation  in  the  decussation  of  very  thick  medullated  fibers. 
They  come  from  the  Nervus  trochlearis,  which,  without  exception  in  the 
animal  kingdom,  decussates  here  on  the  boundary  between  the  midbrain 
and  the  oblongata.  Just  behind  this  begin  the  ventral  decussations  of  the 
cerebellum.  The  most  anterior  belong  to  the  Tractus  cerebello-nucleares 
Trigemini:  the  most  posterior  one  to  the  tract  of  the  Acusticus.  How- 
ever, the  separate  elements  of  the  ventral  decussation  of  the  cerebellum  are 
not  yet  sufficiently  known. 


110  ANATOMY    OF   THE    CENTRAL   NERVOUS    SYSTEM. 

There  are  also  dorsal  decussations  in  the  cerebellum.  They  arise  mostly 
from  the  Tractus  cerebello-spinales,  probably  also  from  cerebellar  nuclei 
(see  Fig.  210). 

Within  the  cerebellum  there  are  everywhere  associated  bundles.  The 
largest  of  these  are  found  in  teleosts,  where  a  large  bundle  of  medullated 
fibers  joins  the  posterior  portion  of  the  cerebellum  with  the  anterior  (Fig. 
86).  Then  there  are  always  numerous  short  association-bundles,  some  of 
which  pass  ventral  to  the  Pur  kin  je  cells  in  the  inner  lamina  and  a  part 
dorsal  to  it  in  the  molecular  lamina.  What  further  connections  are  possible 
through  the  medullated  nerve-processes  may  be  better  studied  in  the 
description  of  the  mammalian  brain. 

To  Summarize. — In  the  cerebellum  we  have  an  organ  into  which  nerve- 
tracts  enter  from  the  interbrain,  the  midbrain,  the  medulla,  and  the  spinal 
cord:  an  organ  that  in  mammals  is  also  indirectly  connected  with  the  cere- 


Fig.  62. — From  the  cerebellum  of  the  minnow:  Phoxinus  laems.  a,  Purkinje 
cells.  6,  Cells  of  the  granular  layer,  of  which  one  sends  its  neuraxons  up  into 
the  association-net  of  the  zona  molecularis  (C). 

brum.  Into  this  organ  pass  bundles  from  several  sensory  cranial  nerves, 
especially  from  the  nerves  of  equilibration. 

Within  the  cerebellum  manifold  connections  are  possible  through  cell- 
processes,  as  well  as  through  contact  with  the  numerous  local  cells. 

It  is  easily  conceivable  that  in  this  range  of  possible  connections  with 
tracts  from  almost  every  part  of  the  brain  is  laid  the  foundation  for  co- 
ordination of  movements  and  for  the  maintenance  of  muscle-tonus:  functions 
which  must  be  ascribed  to  the  cerebellum. 

The  loss  of  the  cerebellum  has  no  vital  significance  in  lower  vertebrates. 
It  appears  that  a  part  of  the  functions  performed  by  it  may  be  suspended,  to 
be  replaced  in  some  way  by  another  part  of  the  brain.  Even  the  minimum 
development  of  the  organ  in  creeping  animals  indicates  that  it  has  essen- 
tially functions  which  in  some  way  are  connected  with  locomotion. 


THE    CEREBELLUM.  Ill 

Though  the  cerebellum  possesses  connections  with  many  parts  of  the 
brain,  it  is  not  traversed  by  a  single  tract  passing  from  lower  to  higher 
levels.  These  all  remain  in  the  base  of  the  oblongata,  thence  to  pass  to 
the  base  of  the  midbrain. 


CHAPTEE   IX. 
THE  MIDBRAIN,  OK  MESENCEPHALON. 

THEEE  is  no  part  of  the  brain  into  which  such  large  tracts  enter,  none 
from  which  so  many  tracts  emerge  for  distribution  to  remote  parts  of  the 
nervous  system,  and  none  within  which  are  furnished  so  many  connections 
between  right  and  left  side  as  the  MIDBRAIN:  THE  MESENCEPHALON  of  the 
lower  vertebrates.  Only  in  mammals,  where  the  cerebrum  is  developed  into 
the  great  organ  peculiar  to  that  class,  does  there  arise  a  brain-segment 
which  contains  still  more  extended  connections  and  still  greater  commissural 
tracts. 


Fig.  63. — Brain  of  the  cod:    Gadus  wgleflnis. 

Even  the  external  appearance  is  suggestive  of  the  significance  of  the 
structure.  The  accompanying  figure  (Fig.  63)  of  the  brain  of  the  cod  shows 
at  once  how  relatively  great  is  the  development  of  the  mesencephalon,  and 
that  it  is  approached  in  size  only  by  the  medulla,  which  is  the  origin  of  the 
large  cranial  nerves.  The  cerebrum  and,  indeed,  even  the  cerebellum — 
always  unusually  large  in  teleosts — are  hardly  to  be  compared  in  size  with 
the  midbrain  and  medulla. 

In  the  description  of  the  midbrain  it  is  advisable  to  differentiate  at  once 
a  roof-segment  and  a  basal  segment.  Throughout  the  entire  animal  king- 
dom the  roof  exhibits  fewer  changes  than  any  other  part  of  the  brain.  The 
(112) 


THE    HIDBBAIX. 


113 


relative  size  only  changes,  and  one  who  is  acquainted  solely  with  the  rela- 
tively small  corpora  quadrigemina  of  man  is  surprised  when  he  sees  the 
immense  optic  lobes  of  a  fish  or  a  bird.  But  the  minute  structure  is  always 
the  same.  In  the  dorsal  layers  of  the  hemisphere — partially  divided  dorsally 
by  a  sagittal  fissure — the  optic  nerve  always  ends.  From  the  ventral  layers 
always  arises  a  system  of  sensory  fibers:  the  deep  marrow,  which  contains, 
among  others,  the  already  described  Tractus  tecto-spinales  et  tecto-bulbares. 

This  is  very  beautifully  seen  in  the  sagittal  section  of  the  brain  of  an 
amphibian  larva,  because  here  scarcely  any  fibers  in  the  midbrain  except 
these  two  tracts  are  medullated. 

The  roof  of  the  midbrain  is  so  large  in  fishes,  and  birds  especially, 


Fig.  64.— Sagittal  section  of  the  brain  of  Axolotl,  the  amblystoma- 
larya  of  Siredon. 


because  it  produces  such  an  unusually  large  opticus.  In  amphibians  and 
reptiles  it  is  also  relatively  larger  than  in  selachians  and  mammals.  The 
ventricle  of  the  midbrain  in  the  first-named  animal  is  correspondingly  large 
(see  Fig.  68),  while  it  is  reduced  to  a  crevice — the  aquasductus  Sylvii — in 
selachians  and  mammals.  The  extension  of  the  roof  in  birds  and  in  the 
teleosts  has  also  led  lateral  pendulous  projection  over  the  base  of  the  mid- 
brain  (see  Fig.  55,  D).  One,  therefore,  sees  the  roof -formation  inclosing  the 
base  externally.  If  one  lay  the  brain  of  a  bird  or  of  a  fish  with  the  base 
up,  he  will  see,  on  either  side,  the  optic,  arising  from  great  white  promi- 
nences, which,  in  spite  of  the  fact  that  they  embrace  the  base,  are,  on 
inspection,  evidently  nothing  else  than  the  strongly  developed  midbrain- 
roof. 


114 


ANATOMY   OF    THE    CENTRAL    NERVOUS    SYSTEM. 


The  Tectum  mesencephali  is  practically  the  ganglion  of  origin  and 
the  terminal  ganglion  for  both  of  the  kinds  of  fibers  mentioned;  also  for 
a  great  number  of  intratectal  association-tracts.  It  receives,  also,  an  afferent 
bundle  from  the  Thalamus,  and  in  birds  and  mammals  such  a  one  from  the 
cerebrum. 

In  the  posterior  portion  of  the  midbrain  lies,  in  all  animals,  a  single 
nucleus,  from  which  fibers  join  the  deep  marrow;  this  nucleus  is  called 
the  Corpus  quadrigeminum  posterius  (Fig.  65).  In  mammals,  where  the 


Central  trigeminus  tract 

Decussation  of  the  peduncles 

iterior  extremity  of  the  motor  \ 
nucleus  of  the  trigeminus      / 

Fillet 
Med.  Tr.  tecto-spin.  cruc. 


Fig.  65. — Frontal  section  through  the  most  posterior  portion  of 
the  midbrain  of  a  lizard. 


anterior  part  of  the  roof  remains  relatively  small,  this  corp.  quad.  post, 
reaches  a  size  almost  equal  to  that  of  the  anterior  bodies. 

In  the  same  manner  in  the  anterior  division  of  the  roof  there  lies  im- 
bedded on  either  side  of  the  middle  line  a  beautifully  outlined,  roundish 
nucleus,  which,  up  to  the  present,  has  only  been  found  in  lower  animals, 
and  whose  demonstration  in  mammals  has  not  yet  been  accomplished: 
Nucleus  prcetectalis. 

The  base  of  the  midbrain  is  formed  of  those  masses  of  fibers  which 
arise  in  the  forebrain  and  interbrain  and  pass  the  midbrain  on  their  way 


THE    MIDBRAIN. 


115 


to  parts  beyond.  Then  there  are  fibers  which  pass  into  the  base  from  their 
origin  in  the  roof.  Finally,  a  number  of  nuclei  have  been  found  there,  from 
which  arise  bundles  which  pass,  in  part,  into  the  cerebellum,  in  part,  to 
the  brain-surface  as  peripheral  nerves:  Oculomotorius,  Trochlearis  (see 
Fig.  68). 

From  the  roof  of  the  midbrain  passes  from  one  side  to  the  other  of 
the  brain  a  large  commissure:  Commissura  posterior  cerebri.  It  lies  in  the 
roof -plate  itself,  and  borders  entirely  upon  the  posterior  wall  of  the  epiphysis 
(see  Figs.  18  and  89). 

The  minute  structure  of  the  roof  of  the  midbrain  is  exactly  known  only 


Fig.  66. — Showing  the  minute  structure  of  the  midbrain-roof.  Two  sections 
placed  side  by  side  for  comparison  of  the  layers.  After  Pedro  R.  y  Cajal.  Right- 
hand  section  from  a  frog.  Note  opticus  fibers  entering  and  ramifying  in  different 
layers.  Sagittal  section  (compare  Fig.  64).  Left-hand  section  from  a  lizard. 
Note  the  cells. 

through  the  researches  of  E.  y  Cajal,  of  Fusari,  and  especially  of  von 
Gehuchten  and  P.  E.  y  Cajal,  in  representatives  of  the  different  classes  of 
vertebrates. 

It  becomes  evident  that  the  different  layers  into  which  the  roof-plate 
may,  in  all  animals,  be  subdivided  arise  in  a  relatively  simple  manner  (see 
Fig.  66). 

Into  the  outer  layer  enter  the  fibers  of  the  optic  nerve  with  innumer- 


116  ANATOMY    OF    THE    CENTRAL   NERVOUS    SYSTEM. 

able  terminal  ramifications.  There  are  similar  nerve-terminations  in  several 
of  the  deeper  layers.  The  terminal  ramifications  come  into  manifold  rela- 
tions with  the  dendrites  of  cells  which  lie  at  various  levels.  A  small  number 
of  such  cells  appear  to  send  fibers  down  into  the  optic  nerve  itself,  but  the 
majority — especially  a  long  layer  of  very  large  cells — send  their  neuraxous 
ventrally,  where  they  form  a  definite  layer  of  the  deep  medullary  layer: 
Stratum  medullare  profundum.  But  into  this  layer,  as  into  the  optic  layer, 
numerous  fibers  enter  from  other  terminal  ganglia.  Through  this  structure 
there  arises  an  extraordinarily  great  opportunity  for  the  transmission  of 
light-impressions  to  the  general  sensory  tract,  since  the  deep  medullary  layer, 
as  far  as  now  known,  is  in  connection  with  ends  of  other  sensory  nerves. 

Eefer  to  Figs.  64  and  71,  and  see  how,  at  the  posterior  end  of  the  mid- 
brain,  the  complex  of  Tractus  tecto-spinales  et  tecto-bulbares  just  anterior 


to  the  cerebellum  rises  abruptly  into  the  midbrain  and  there  enters  the  deep 
medullated  layer.  There  we  have  again  found  connection  with  a  bundle 
already  familiar,  and  may  turn  our  attention  to  others. 

Naturally,  it  is  not  very  easy  in  all  the  fiber-systems  which  fill  the 
ventral  portion  of  the  midbrain  to  recognize  the  separate  relations.  To 
solve  this  problem  in  adult  animals  seems  quite  impossible.  As  most  wel- 
come simple  objects,  the  larvae  of  amphibians  offer  themselves.  Here  the 
system  of  the  deep  medullary  stratum  develops  itself  before  all  other  fiber- 
systems  of  the  midbrain,  even  earlier  than  the  optic  nerve.  This  layer  has 
medullary  sheaths  at  a  time  when  no  other  system  in  this  region  is  medul- 
lated, except,  probably,  the  nuclei  of  the  cranial  nerves.  If  one,  in  observing 
a  frontal  section,  passes  from  the  ventricular  epithelium  outward,  one 
comes  first  upon  a  layer  of  loose  tissue  with  few  cells, —  the  Ependym, — then 
a  simple  tissue  with  large  ganglion-cells,  and  beyond  it  into  the  only  medul- 


THE    MIDBRAIX. 


117 


lated  layer  of  the  roof-plate:  the  stratum  medullare  profundum.  Still  be- 
yond that  one  recognizes  cells  and  thin  non-medullated  fibers.  What  be- 
comes of  the  medullated  layer  may  be  easily  understood  (see  Fig.  67).  A 
part  passes  direct  to  the  side  of  the  midbrain  and  down  to  the  base,  thence 
posteriorly:  a  second  part  goes  the  same  way,  except  that  it  first  crosses 
the  median  line  before  it  turns  downward.  This  decussation  was  formerly 
called  Commissura  ansulata.  These  two  parts  together  represent  the  lateral 
division  of  the  deep  medullary  layer.  The  fibers  of  the  median  division 
which  lies  next  to  the  ventricle  do  not  turn  toward  the  base  of  the  midbrain. 


Valvula  cerebelli  — 


Gangl.  mesenceph.  lat. . 

Median  fasciculus   of  the! 
deep  medullary  layer/  ~ 
Nncl.  N.  oculo-mot.  .. 


Tr.  lobi  inf.  ad  cerebell. 


Lateral     portion    of  the! 
deep  medullary  layer/ 


Fig.  68.— Frontal,  section  through  the  midbrain  of  a  teleost,  Rhodeus  amarus. 


For  a  short  distance  they  pass  parallel  to  the  ventricular  wall  and  then 
divide,  like  the  lateral  portion,  into  a  direct  and  crossed  bundle. 

The  direct  portion  ends  mostly  in  a  ganglion, — Ganglion  laterale 
mesencephali  (see  Fig.  68);  the  crossed  portion  encircles  the  floor  of  the 
ventricle,  which  presents  here  only  a  narrow  cleft,  and  forms  under  it  in 
beautifully  plaited  lines  the  tegmental  decussation  (HaubenJcreutzung). 
Afterward  it  passes  posteriorly  close  to  the  middle  line>  ventral  to  the  fibers 
of  the  posterior  longitudinal  bundle  (see  Fig.  91). 

Thus,  all  of  these  are  bundles  which  connect  the  deep  layers  of  the 
midroof  with  more  posterior  segments.  Most  of  them  end  in  the  medulla, 


118 


ANATOMY    OF    THE    CENTEAL   NERVOUS    SYSTEM. 


in  the  nuclei  of  the  posterior  columns,  and  in  the  gray  matter  of  the  spinal 
cord:  Tractus  tecto-spinales  et  tecto-bulbares.  In  adult  animals  the  deep 
medullary  layer  of  the  midbrain  may  be  best  studied  where  it  is  best 
developed:  i.e.,  in  birds  or  in  fishes.  The  teleosts  present  the  especial  ad- 
vantage that  the  region  in  which  the  Stratum  medullare  prof,  lies  is  rela- 
tively simple  in  structure;  so  that  the  tracing  of  the  fibers  is  facilitated. 
If  one  becomes  once  familiar  with  the  relations  in  teleosts  he  may  find  them 
readily  again  in  any  of  the  higher  vertebrates. 

In  Fig.  68  one  may  find  several  of  the  structures  above  mentioned.  The 
tegmental  decussation  is  not,  however,  to  be  readily  found.  In  the  enor- 
mous extension  of  the  roof,  which  is  found  in  the  teleosts,  these  fibers  have 
come  into  another  position.  They  lie  now  directly  upon  the  decussation 
which  the  lateral  position  of  the  medullated  stratum  makes,  and  thus  in- 


Optic  stratum 


Fig.  69. — Transverse  section  through  the  midbrain  of  a  toad:    Buf.  tin. 

creases  the  commissura  ansulata.  In  horizontal  sections  one  may  readily 
separate  the  two  parts  of  the  commissure  (see  Fig.  91). 

The  fiber-system  of  the  medullary  stratum  from  the  roof  of  the  mid- 
brain  fills  a  large  part  of  the  basal  portion  of  that  brain-segment,  encircling 
and  traversing  it.  Because  of  the  great  number  of  transverse  fibers,  the  base 
of  the  midbrain  has  been  called  the  Pars  commissuralis. 

The  roof  of  the  midbrain  gives  origin  to  still  another  system  from  the 
same  layer:  viz.,  the  fibers  which,  taken  together,  are  much  greater  than 
parts  mentioned,  and  which,  throughout  the  whole  rbof  region,  pass  in 
lateral  direction  from  right  to  left  or  vice  versa.  Through  these  fibers  there 
is  formed  in  the  median  line  the  dorsal  decussation  of  the  midbrain.  The 
whole  structure  is  the  Lamina  commissuralis  mesencephali.  This  decussa- 
tion is  exceedingly  constant,  and  from  Petromyzon  to  man  it  is  always 
present.  In  Fig.  68  it  may  be  seen  as  a  shaded  inner  layer  of  the  roof.  It 


THE    HIDBKAIX. 


119 


joins  anteriorly  with  the  transverse  fibers,  which,  as  Commissura  posterior, 
pass  along  the  frontal  end  of  the  midbrain-roof  (Fig.  69).  But,  through  the 
narrower  caliber  of  its  fibers  and  their  somewhat  more  dorsal  position,  the 
bundle  is  always  readily  distinguished  from  the  posterior  commissure. 

The  optic  nerve  arises,  in  all  lower  vertebrates,  chiefly  from  the  roof  of 
the  midbrain.  Figs.  64  and  70  give  a  good  view  of  this  origin. 

Only  in  the  higher  mammals  does  the  optieus  origin  in  the  ganglia  of 
the  thalamus  appear  to  play  a  greater  role.  The  roof  of  the  midbrain  is  a 
segment  of  a  sphere.  From  the  ventral  chiasma  a  curving  tract  of  manifold 
bundles  encircling  the  whole  mass  of  the  midbrain  passes  to  the  Optieus. 


Fig.  70. — Transverse  section  of  Rhodeus  amarus  through  the  region  of  the 
chiasma.  Note  that  the  Tectum  mesencephali  covers  the  Optieus.  The  median 
portion  of  the  figure  belongs  to  the  thalamencephalon. 


Most  of  the  bundles  lie  near  the  surface,  and,  like  the  partially  flexed  fingers 
of  a  hand,  inclose  the  spherical  mass;  but  a  smaller  number  of  bundles, 
especially  those  which  are  destined  for  the  more  posterior  portion  of  the 
Optieus,  turn  inward  just  before  reaching  the  roof  of  the  midbrain,  and 
pass  toward  their  terminus,  breaking  through  the  basis  of  the  midbrain- 
roof,  thus,  in  a  measure,  passing  under  it. 

These  different  bundles  have  been  described  as  different  "roots":  viz., 
as  "median,  lateral,"  etc.;  but  this  has  little  to  recommend  it,  for,  though 
some  of  the  bundles  vary  their  course  somewhat,  they  all  pass  to  the  same 
end. 


120 


ANATOMY    OF    THE    CENTRAL    NERVOUS    SYSTEM. 


Since  the  optic  tract  enters  the  frontal  end  of  the  midbrain,  one 
will  meet  it  only  in  sections  which  are  cut  far  forward.  Such  a  section  (as 
shown  in  Fig.  70)  encroaches  upon  the  interbrain. 

The  Tectum  mesencephali  is,  in  all  lower  vertebrates,  brought  into 
intimate  relations  with  the  great  nuclei  of  the  interbrain  (thalamen- 
cephalon)  through  a  large  bundle:  the  Tractus  tecto-thalamicus.  The 
bundle  is  so  large  that  it  will  doubtless  be  found  in  mammals  also.  It  is 
lost  between  the  layers  of  the  roof.  The  cerebral  connections  probably  exist 
in  reptiles;  in  birds  and  mammals,  however,  its  existence  is  certain. 

Important  in  the  investigation  of  the  brain  of  lower  vertebrates  is  the 
large-celled  roof-nucleus  (Daclikerri).  The  nucleus  in  question  lies  close  on 


Fig.  71. — Sagittal  section  of  a  lizard-brain,  showing  the  position  of  the 
nuc.  lat.  mesencephali;  also  showing  well  the  different  bundles  of  the  Opticus 
and  the  course  of  the  fibers  from  the  deep  medullary  stratum  into  the  fillet. 


either  side  of  the  median  line,  but  does  not  occupy  the  whole  length  of  the 
roof.  It  is  not  present  in  mammals,  but  one  meets  there  a  group  of  quite 
similar  cells,  which  degeneration-experiments  have  shown  to  belong  to  the 
fiber-system  of  the  Trigeminus:  Radix  mesencephalica  Nervi  V.  It  has 
not  been  demonstrated,  however,  that  the  origin  of  the  midbrain-root  of  the 
Fifth  nerve  is  a  homologue  of  the  Dachkern  in  question. 

The  basis  of  the  midbrain  is  distinguished  by  the  numerous  already 
described  decussations  which  lie  in  it,  but  the  fact  that  several  important 
bundles  pass  into  it  from  the  interbrain,  and  finally  by  the  presence  of 
several  separate  nuclei. 


THE    MIDBRAIX.  121 

In  birds  and  fishes  where  it  is  widely  spread  out  on  account  of  the  large 
roof,  where  also  the  ventricle  comes  into  relation  with  not  a  small  part,  it  is 
especially  favorable  for  study.  One  recognizes  at  once  that  the  central  gray, 
which  everywhere  incloses  the  ventricle,  covers  everywhere  the  surface  of  the 
midbrain-base,  which  lies  next  the  ventricle.  In  this  gray  matter — that  is, 
in  the  dorsal  portion  of  the  midbrain-base — lie  several  important  nuclei. 
Near  either  side  of  the  median  line  may  always  be  seen  a  number  of  small 
masses  of  cells,  which  send  out  ventrally  the  fibers  of  the  Nervus  oculo- 
motorius  (see  Fig.  68).  Even  in  the  lowest  vertebrates  these  leave  the  base 
of  the  brain,  always  at  the  same  place,  as  two  not  unimportant  nerves,  which 
turn  toward  the  eye-cavity.  Just  posterior  to  the  nucleus  of  the  Oculomo- 
torius  one  finds  aggregations  of  cells  (Fig.  65)  from  which  the  Trochlearis 
arises.  In  all  animals  yet  studied  the  nerve  crosses  to  the  other  side  in  the 
Velum  medullare  posticum  (Fig.  60).  In  order  to  reach  this  dorsally  located 
decussation,  its  fibers  must,  just  after  their  origin,  pass  somewhat  back- 
ward and  then  turn  dorsally.  Thus,  the  nerve  which  passes  off  quite 
dorsally  always  appears  in  the  narrow  crevice  which  remains  between  the 
midbrain-roof  and  the  cerebellum  (see  Figs.  56  and  74). 

Lateral  from  the  nuclear  origin  of  this  nerve  there  lies,  in  the  midst  of 
the  central  gray,  a  large  nucleus:  the  Nucleus  lateralis  mesencephali.  The 
thin  layer  of  nerve-netted  gray  matter  around  the  aqueduct  in  mammals 
scarcely  suggests  what  important  structures  are  here  represented  in  a  process 
of  retrogression.  If  one  dissects  off  the  roof  of  the  teleostean  midbrain, 
one  will  see,  under  the  same,  the  protruded  part  of  the  cerebellum  as  a 
large  evagination  divided  in  the  median  line  (see  Fig.  86).  Laterally  from 
this  one  finds  on  either  side  an  elongated,  somewhat  curved  projection, 
which  may  not,  like  the  cerebellum,  be  lifted  from  the  floor  of  the  mid- 
brain;  in  fact,  it  belongs  to  this.  This  growth  was  known  to  the  old  anatom- 
ists, and  was  designated  by  them  as  Torus  semicircularis.  The  Torus  arises 
through  the  location  of  the  lateral  mesencephalic  nucleus  (especially  large 
in  fishes)  in  the  lateral  part  of  the  central  gray  of  the  midbrain.  The  same 
nucleus  is  also  demonstrable  in  birds,  even  though  it  'does  not  reach  in  them 
the  relative  size  which  it  has  in  fishes.  In  selachia  its  presence  is,  to  me, 
doubtful;  but  in  reptiles  it  is  evident,  and  in  amphibia  it  is,  through  the 
location  at  least,  to  be  recognized  (Fig.  72).  From  the  nucleus  lateralis 
mesencephali  arises  a  large  bundle:  the  lateral  longitudinal  bundle.  It  may 
be  followed  through  the  entire  medulla  oblongata,  and  probably  passes  into 
the  lateral  columns  of  the  spinal  cord. 

That  a  part  of  the  longitudinal  fiber-system  in  the  midbrain-base  arises 
from  the  thalamus  (Fig.  71)  was  mentioned  above.  Three  of  the  bundles 
which  lie  here  deserve  especial  mention  before  we  consider  the  thalamus, 
because  they  give  to  the  medullary  white  matter  of  the  base  its  characteristic 


122 


ANATOMY    OF    THE    CENTRAL    NERVOUS    SYSTEM. 


feature.  The  first  is  the  Fasciculus  longitudinalis  posterior  (Fig.  44).  It 
arises  with  its  most  anterior  fibers  from  a  single  nucleus  of  the  most  posterior 
part  of  the  Thalamus,  but  reinforces  itself  in  its  backward  course,  while  it 
passes  the  nucleus  of  the  Oculomotorius.  The  bundle  lies  on  either  side  of 
the  middle  line  quite  dorsally,  partly  imbedded  in  the  nuclei  in  question  and 
partly  ventral  to  them  (Fig.  65).  In  a  similar  way  from  a  nucleus  which  is 
readily  to  be  seen  in  the  ventral  part  of  the  thalamencephalon  in  all  lower 
vertebrates — Nucleus  tegmenti — arises  the  Tractus  tegmento-cerebellaris, — 
the  peduncle  of  the  cerebellum.  It  traverses  the  midbrain  for  only  a  short 


Fig.  72. — Sagittal  section  of  brain  of  chick  on  eighth  day  after  hatching, 
showing  origin  of  the  Fasc.  long,  lateralis. 


distance,  and  crosses  to  the  other  side  just  behind  the  last  roots  of  the  Oculo- 
motorius (see  Fig.  65).  The  decussation  of  the  Tractus  tegmento-cere- 
bellaris lies  dorsal  to  the  decussation  of  the  tegmental  tract  from  the  roof: 
Commissura  ansulata. 

The  third  longitudinal  fasciculus  of  the  midbrain-basis  arises  from  the 
commissura  posterior  (Figs.  69  and  73),  whose  limbs  turn  backward  after 
the  decussation  quite  anterior  to  the  midbrain-roof,  describing  the  out- 
line of  a  horseshoe.  The  posterior  end  is  still  unknown.  There  is  strong 
evidence  that  in  the  lateral  parts  of  the  posterior  longitudinal  bundle  fibers 
from  that  commissure  pass  far  back.  According  to  Kolliker  and  others, 


THE    MIDBEAIN. 


123 


the  whole  system  arises  from  a  nucleus  lying  in  the  region  of  the  Nucleus 
fasciculi  posterior.  The  author  is  unable  to  differentiate  a  separate  nucleus. 
The  relation  of  the  posterior  longitudinal  fasciculus  to  the  posterior  com- 
missure requires  further  elucidation.  This  has  been  retarded,  because  both 
bundles  are  so  difficult  to  bring  to  degeneration  in  continuo. 

Quite  ventral  in  the  anterior  part  of  the  midbrain-base  lies  a  flat  len- 
ticular ganglion,  which  receives  bundles,  among  which  are  some  from  the 
Corp.  striata  of  the  cerebrum.  So  far  as  the  author  sees,  it  is  best  denned 
in  the  reptiles  and  birds.  The  mammals  have,  in  the  same  location,  two 
ganglia:  one  behind  the  other,  the  anterior  one  being  called  Corpus  sub- 
ihalamicum,  and  the  posterior  Substantia  nigra.  Which  one  of  these  cor- 


'Outer  and    inner   laminae   of 
.     opticus 


Gray  matter  of  central  canal 

(  Decussation  of  the  deep  medul- 
\     lary  stratum 

/Median    portion  of  the    deep 
\     medullary  stratum 


(  Lateral  portion  of  the 
\     deep  med.  stratum 
Posterior  commissure 
Fasc.  long.  .post. 
Options 
Nucl.  prof.  lat. 

Nucl.  prof.  med. 
Gangl.  ventr.  teguienti 


Fig.  73. — Frontal  section  through  the  midbrain  of  Lacerta. 


responds  to  the  basal  ganglion  of  lower  vertebrates  is  yet  uncertain,  the 
term  Ganglion  ventrale  tegmenti  being  used  to  designate  the  structure  (see 
Fig.  73). 

To  the  special  ganglia  of  the  thalamencephalon  must  be  reckoned  two 
not  clearly  defined  cell-aggregations:  one  lying  in  the  lateral  portion  of 
the  base  and  one  close  beside  the  median  line.  Into  both  pass  portions  of 
the  deep  medullary  stratum:  into  the  lateral  one,  the  uncrossed  fibers,  and 
into  the  median  one  the  crossed  fibers  of  the  median  portion  of  the  deep 
medullary  stratum.  The  nuclei  may  be  designated  as  the  lateral  and  median 
deep  midbrain-nudei  (nuc.  pro  fund.  lat.  and  nuc.  profund.  med.,  Fig.  73). 

The  midbrain-base  is  naturally,  in  fishes,  traversed  also  by  those  fibers 


124  .ANATOMY    OF   THE    CENTRAL    NERYOTJS    SYSTEM. 

which  pass  from  the  thalamus  to  the  cerebellum;  furthermore,  fibers  from 
the  Decussatio  transversa  (Fig.  72),  which  cross  posterior  to  the  chiasma 
and  turn  backward  to  the  midbrain-wall  on  either  side  until  they  reach 
the  most  posterior  region  of  the  midbrain-roof,  probably  ending  in  the 
ganglia  of  the  posterior  quadrigeminal  bodies  or  in  the  Ganglion  isthmi. 

Having  presented  the  gradual  development  of  the  mesencephalon,  let 
us,  without  a  more  detailed  account,  turn  to  a  summary  of  the  most  im- 
portant features. 

Summary. — From  the  roof  of  the  mesencephalon  arises  the  optic  tract 
from  cells  which,  through  their  dendritic  processes  (Endstaiteri),  are  in  com- 
munication with  the  great  roof  commissure  and  with  the  bundles  to  the 
sensory  terminal  nuclei  in  the  oblongata  and  the  spinal  cord.  From  the 
gray  matter  ventral  to  the  aqueduct  arise  fibers  of  the  Nervus  oculo-motorius 
and  of  the  Fasciculus  longitudinalis. 

The  base  is  occupied  mostly  with  longitudinal  bundles,  tracts,  and 
fasciculi  to  the  spinal  cord  and  to  the  cerebellum;  and  the  whole  is  em- 
braced ventrally  by  the  decussation  of  the  deep  medullary  stratum  and 
laterally  by  the  uncrossed  fibers  of  the  same, — the  fillet. 

The  structure  of  the  midbrain  is,  as  far  as  known,  in  all  animals  the 
same,  except  that  those  portions  of  the  fibers  which  pass  downward  from 
the  roof  of  the  organ, — i.e.,  the  Tractus  opticus  and  the  fillet, — are  much 
more  highly  developed  in  fishes  and  birds  than  in  mammals.  In  the  latter, 
therefore,  there  has  taken  place  a  relative  retrogressive  development. 

In  other  places  a  relative  increase  of  the  volume  of  the  midbrain  has 
taken  place;  not,  however,  conditioned  upon  a  change  in  the  structure  of  the 
midbrain  itself, — that  remains  the  same, — but  upon  the  tracts  which  pass 
through  the  organ.  In  mammals  large  tracts  arise  destined  for  the  pons  or 
spinal  cord.  These  tracts  find  no  room  in  the  structure  described  above 
as  typical  for  lower  vertebrates.  They  pass  quite  ventral  to  that,  giving  rise 
to  a  new  external  ventral  layer:  the  cerebral  peduncles.  Lying  dorsal  to  this 
is  the  tegmental  system,  common  to  all  vertebrates;  the  cerebral  peduncles 
represent  a  novum  additum  which  appears  only  late  in  the  animal  kingdom. 

So  the  midbrain  offers  again  a  good  example  of  the  fact  that  in  the 
animal  series  (Taxonomic  Series)  no  one  segment  of  the  brain  undergoes 
a  step-by-step  progressive  development  which  is  even  approximately  parallel 
to  the  rank  of  the  animal  as  determined  by  its  general  structure.  There  is 
a  particular  organ  gradually  developed,  which  may  be  highly  developed  in 
organisms  of  median  rank,  while  in  organisms  of  higher  rank  it  may  be 
weakly  developed,  as  we  have  seen  to  be  the  case  in  the  midbrain.  The 
case  may  be  further  complicated  by  the  association,  here  and  there,  of  new 
tracts  arising  in  brain-segments  which,  in  particular  classes,  are  especially 
developed. 


CHAPTEK   X. 
THE  INTERBRAIN  :    THE  THALAMEXCEPHALON. 

THE  anatomical  apparatus  which  has  been  described  is  so  constructed 
that  it  may  be  looked  upon  as,  in  the  main,  complete  in  itself.  Only  a  very 
few  bundles  pass  anteriorly  from  the  organs  above  described.  Moreover, 
in  the  lower  vertebrates  at  least  only  a  few  small  tracts  pass  from  those 
brain-segments  anterior  to  the  midbrain  into  the  ganglia  which  lie  in  the 
midbrain  and  oblongata,  or  into  the  spinal  centers.  Consequently,  fishes, 
amphibians,  and  reptiles  never  show  so  marked  derangement  of  functions 
where  all  of  the  brain  anterior  to  the  posterior  commissure  is  removed  as 


Fig.  74. — Brain  of  a  Nile  crocodile,  natural  size.  The  cerebrum  covers  the 
thalamus  anteriorly;  the  Tractus  opticus  covers  it  laterally;  so  that  only  a  small 
part  of  the  hypothalamus  remains  visible. 


when  the  midbrain,  with  its  great  association-bundles  and  important  tracts, 
is  injured  or  when  one  injures  the  oblongata  or  the  spinal  cord. 

Eegarding  the  .physiological  significance  of  that  part  of  the  brain  be- 
tween the  midbrain  and  the  cerebrum — viz.,  the  Thalamencephalon — we 
know  practically  nothing  and  we  stand  only  on  the  threshold  of  morpho- 
logical knowledge. 

Doubtless,  however,  the  thalamencephalon  is  an  important  segment  of 
the  brain.  Since  from  Petromyzon  up  through  the  vertebrates,  however 
weakly  one  or  the  other  brain-segment  may  be  developed,  one  imiformly 
finds  the  interbrain  anterior  to  the  midbrain.  In  the  external  view  of  the 
brain  it  is  scarcely  visible,  because,  even  in  those  cases  where  it  is  not  en- 
mantled  by  the  hemispheres,  still  the  midbrain-roof  protrudes  beyond  it, 
and,  furthermore,  it  is  completely  covered  laterally  through  the  great  fiber- 

(125) 


126 


ANATOMY    OF   THE    CENTRAL   NERVOUS    SYSTEM. 


system  of  the  optic  tract,  which  passes  down  to  the  chiasma  from  the  roof 
of  the  midbrain. 

The  best  starting-point  is  the  very  simply  constructed  thalamen- 
cephalon  of  the  amphibian.  It  is  an  elongated  body  of  oval  cross-section, 
continuous  anteriorly  with  the  prosencephalon  and  posteriorly  with  the 
mesencephalon.  Close  behind  the  plexus  chorioides  of  the  cerebrum  is 
located  on  either  side  a  small  ganglion, — Corpus  habenulce, — and  this 
division  is  designated  the  epithalamus.  On  the  ventral  side  lie  several 
prominences  and  aggregations  of  ganglia  which*  are,  in  part,  readily  dis- 
tinguished from  the  rest  of  the  thalamus,  and  are  grouped  together  as  the 
Hypothalamus.  The  principal  body  which  lies  between  these  two  just 


Fig.  75.— Section  through  the  Diencephalon  of  Bufo:    toad. 

named  retains  the  name  Thalamus.  These  three  divisions  are  practically 
demonstrable  in  all  vertebrates,  but  the  epithalamus  alone  is  uniform  in  its 
structure,  the  other  divisions  varying  much  in  different  genera. 

The  central  cavity  of  the  thalamencephalon  is  closed  dorsally  with 
several  folds  of  the  same  epithelial  plate  as  had  formerly  constituted  the 
entire  encephalon  (see  Figs.  18  and  20).  Besides  this,  the  roof  contains  the 
fibers  of  a  small  commissure:  Commissura  habenularis. 

Anteriorly  the  interbrain  is  separated  from  the  cranial  cavity  by  the 
Lamina  terminalis  (see  Chapter  IV,  page  49).  It  is  always  narrow,  and  on 
either  side  of  it  an  opening  leads  into  the  central  cavity  of  the  hemispheres, 
which  even  in  the  embryonic  period  are  evaginated  dorso-laterally  from 
this  location. 


THE    IXTERBRAIX    OR    THALAMEXCEPHALON. 


127 


The  lamina  terminalis  of  the  brain,  before  turning  backward  to  form 
the  roof  of  the  interbrain,  passes  first  a  short  distance  dorsally, — Lamina 
supraneuroporica, — and  then  falls  in  the  usually  sail-like,  pendulous  Tela 
chorioidea,  from  which,  through  anteriorly-directed  evaginations,  the  Plexus 
chorioidei  of  the  ventricle  is  formed.  In  several  amphibians  (Fig.  55,  B) 
and  in  the  Dipnoi,  whose  brain  can  scarcely  be  differentiated  from  the  typ- 
ical amphibian  brain,  the  Tela  grows  exuberantly  into  the  central  cavity 
of  the  interbrain  by  the  addition  of  numerous  tap-like  processes.  Close  to 
the  epithelium  there  always  lies  a  rich,  vascular  plexus.  It  is  probable  that 
the  structure  is  an  organ  of  secretion.  Posterior  to  the  Tela  chorioidea  are 
one,  or  frequently  several,  dorsally  directed  projections  called  Paraphysis  and 
EpipJiysis,  according  to  their  relative  location  (see  Figs.  76  and  86). 


Fig.  76. — Median  sagittal  section  through  the  brain  of  the  lizard:    Taranus  griseus. 


Just  anterior  to  the  epiphyseal  evagination,  the  entrance  to  which  i& 
not  shown  in  the  figure,  lies  regularly  the  Commissura  habenularis.  It  be- 
longs to  the  system  of  fibers  which  pass  into  the  Ganglia  habenulce  from  the 
posterior  olfactory  region,  and  will  be  considered  later. 

The  epiphyseal  tube  is  very  constant.  In  several  selachians  and  in 
many  reptiles  this  structure  passes  through  a  hole  in  the  skull  to  a  sense- 
organ  under  the  skin  which  has  a  striking  resemblance  to  an  eye.  One  can 
recognize  in  this  impaired  parietal  organ  a  cornea,  a  lens,  a  retina,  and, 
below  this,  a  pigmental  layer.  We  are  indebted  to  Graf  and  Spencer  for  its 
discovery.  In  other  vertebrates  one  finds  in  the  adult  stage  no  connection 
between  the  epiphyseal  tube  and  the  sense-organ.  The  epiphysis  has  with- 
drawn within  the  skull,  and  the  parietal  eye  is  so  completely  lost  in  the 
amphibian  and  reptilian  transitional  forms  that  in  birds  and  mammals  no 


128 


ANATOMY   OF   THE    CENTRAL    NERVOUS    SYSTEM. 


trace  of  it  remains.    The  blunt,  often  enlarged  end  of  the  tube  remains  as 
a  little  tubercle, — the  pineal  gland, — just  anterior  to  the  midbrain. 

The  base  of  the  thalamencephalon  is,  in  the  median  line  at  least, 
separated  from  the  skull  by  only  a  thin  membrane.  Within  it  and  under 
it  pass  important  systems  of  transverse  fibers,  and  just  at  the  middle  line 
the  hypothalamus  is  thickened  into  a  structure  of  varying  form.  Ventral 
to  the  commissural  region  of  the  cerebrum  the  lamina  terminalis  has  a 
small  evagination  anterior  to  the  chiasma:  the  Recessus  prceopticus.  It 
then  covers  the  basal  wall  over  the  chiasma,  through  which  it  is 
strongly  curved  inward  (Fig.  76),  and  then  curves  outward,  forming  the 
Recessus  postopticus.  Still  farther  posterior  follows  always  a  deep  recess, 


Fig.  77. — Sagittal  section  through  the  infundibular  region  of  a  shark: 
Scyllium  canieula. 


which  often  ends  in  a  narrow,  often  thread-like  tube:  the  infundib- 
ulum  or  Recessus  infundibularis.  The  projection  which  this  makes  upon 
the  base  of  the  brain  is  called  the  Tuber  cinereum.  To  the  terminal  tube 
of  the  infundibulum  is  applied  the  hypophysis:  an  outgrowth  from  the 
oral  epithelium  to  the  base  of  the  skull.  In  mammals  it  grows  so  fast  to  the 
infundibulum  that  it  is  customary  to  refer  to  the  end  of  the  infundibulum 
as  the  cranial  part  of  the  hypophysis. 

Kupffer  made  a  discovery  a  few  years  ago  that  is  destined  to  throw  new 
light  on  the  significance  of  this  structure.  In  the  embryos  of  lower  verte- 
brates— Petromyzon,  sturgeon,  and  others — there  exists,  for  a  period,  a 
peculiar  evagination  from  the  dorsal  side  of  the  primitive  pharynx  and 
directed  forward.  He  called  this  the  preoral  gut. 


THE    IXTERBEAIX    OR    THALAMEXCEPHALOX.  129 

It  is  known  that  in  the  sturgeon  a  passage  leads  from  the  exterior  into 
this  preoral  gut:  i.e.,  the  fundament  of  a  separate  mouth  is  established  over 
the  permanent  mouth.  This  whole  structure — the  preoral  cavity  and  the 
preoral  gut,  into  which  it  leads — becomes  the  hypophysis.  According  to 
Kupffer,  the  evagination  from  the  oral  cavity  of  craniate  vertebrates — the 
hypophysis — is  a  vestige  of  this  old  preoral  cavity. 

In  lower  vertebrates  dorsal  to  the  infundibulum  the  posterior  wall  of 
the  infundibulum  is  evaginated  into  a  long,  narrow  epithelial  tube  whose 
walls  are  thrown  into  numerous  folds  through  the  pressure  of  numerous 
blood-vessels.  The  structure  is  called  the  Saccus  vasculosus  (see  Figs.  59 
and  77).  When  the  posterior  end  of  the  ventral  wall  of  the  interbrain  joins 
to  the  base  of  the  midbrain  one  always  finds  a  farther  small  evagination: 


Fig.  78. — Horizontal  section  through  the  hypophysis  of  the  ray:    Raja  clavata. 

the  Recessus  mammillaris.    In  selachia  it  contains  large  ridges  and  nodules 
of  epithelium,  and  forms  a  richly  vascular  structure  evidently  functional. 

Now  that  the  dorsal  and  ventral  portion  of  the  interbrain  have  been 
described,  we  may  turn  to  the  consideration  of  the  lateral  portions.  Close 
to  the  epithelial  roof  there  lie  the  Ganglia  habenulce,  one  on  either  side,  the 
distinctive  ganglia  of  the  Epithalamus  (Fig.  75).  In  many  of  the  lower 
vertebrates  there  is  a  difference  in  the  size  of  the  two  ganglia;  otherwise, 
however,  the  Ggl.  habenulae  offer  a  good  example  of  a  markedly  constant 
brain-structure,  varying  neither  through  progression  nor  retrogression. 
From  Petromyzon  to  the  mammals  one  always  finds  them  on  either  side  and 
a  little  to  the  front  of  the  epiphyseal  process.  They  consist  of  two  bodies, — 
a  lateral  and  a  median, — and  are  always  separated  from  the  epiphyseal  sac 
posteriorly  by  the  Commissura  habenularis  (Figs.  76,  79,  86).  In  am- 


130 


ANATOMY    OF    THE    CENTRAL   NERVOUS    SYSTEM. 


phibians  and  reptiles  where  the  other  ganglia  of  the  thalamns  are  only 
slightly  developed  relatively,  or  in  fishes  where  they  are  placed  more  to 
the  ventral  position,  the  Ggl.  habenulae  occupy  a  position  in  front  of  all  the 
other  interbrain-ganglia.  When  in  birds  and  mammals  the  other  con- 


Fig.  79. — Horizontal  section  through  the  Gang,  habenulae  of  a  turtle: 
Emys  europ. 


stituents  of  the  thalamencephalon  develop  more  and  more,  they  press  the 
epithalamus  somewhat  back;  so  that  the  whole  remaining  part* of  the 
interbrain  lies  between  it  and  the  forebrain.  The  relative  location  of  the 
epiphysis  remains,  in  the  meantime,  unaffected. 


Fig.  80. — Sagittal  section  through  the  brain  of  Triton,  lateral  from  the 
median  line,  showing  the  Fasciculus  retroflexus;  also  the  Tr.  Strio-thalamicus 
ending  in  three  places  in  the  interbrain. 


The  tracts  which  pass  to  the  epithalamus  are  as  constant  as  the  develop- 
ment. First,  it  always  receives  anteriorly  from  the  olfactory  region  of  the 
cerebrum  an  afferent  tract:  Tractus  olfacto-habenularis.  To  this  is 
associated  in  those  vertebrates  above  the  amphibia  a  bundle  from  cerebral 


THE   IXTEBBBAIX   OK   THALAMENCEPHALON. 


131 


cortex:  Tractus  cortico-liabenularis.  Both  together  form  the  Tcenia 
ilialami  (see  Fig.  100).  Several  smaller  afferent  bundles  need  not  be  men- 
tioned. Eemember  simply,  that  in  the  Ggl.  habenulaB  an  important  con- 
necting bundle  ends,  which  is  composed  of  fibers  from  the  posterior  olfactory 
lobe  and  fibers  to  the  olfactory  cortex. 

A  large  part  of  the  fibers  of  the  Ta?nia  thalami  end,  not  direct  in 
.ganglia  of  the  same  side,  but  cross  to  the  one  on  the  opposite  side  through 
the  Commissura  habenularis.  The  tasnia  consists  of  a  medullated  and  a 


Opticus  med.  fas. 


Tr.  haben.-pedunc. 


Nucl.  rotundus 


Corp.  genie,  lat.  — 


Tr.  strio-thalamicus 


Fig.  81. — Frontal  section  through  the  dorsal  portion  of  the  thalamus  opticus 
of  the  "blind  snake" :     Anguis  fragilis.     Golgi  method. 


non-medullated  portion;  the  same  is  true  of  the  commissure.  Figs.  99  and 
100  show  the  plan  of  the  connection  of  the  olfactory  apparatus  and  the 
Ggl.  habenulae. 

The  more  median  of  the  two  ganglia  sends  out  a  bundle  ventrally: 
Tractus  habenulo-peduncularis,  or  Fasciculus  retroftexus  (see  Figs.  64  and 
80).  Its  fibers  traverse  the  whole  base  of  interbrain  and  midbrain  and  end 
not  far  posterior  to  the  Oculomotorius  in  a  small  ganglion  lying  quite  ven- 
tral in  the  base  of  the  medulla,  in  the  Corpus  interpedunculare  (Fig.  65). 
Here  they  break  up,  and  their  terminal  fibers  decussate  with  those  of  the 


132  ANATOMY   OF   THE    CENTRAL   NERVOUS    SYSTEM. 

other  side.  The  fasciculus  and  the  corpus  interpedunculare  are  absolutely 
constant  throughout  the  whole  vertebrate  series. 

The  ganglia  peculiar  to  the  thalamus  may  only  be  sharply  differentiated 
from  those  of  the  hypothalamus  in  the  mammals  and  birds;  in  lower  verte- 
brates the  two  regions  merge  into  one  another. 

To  the  author  the  Thalamus  of  the  reptile  is  best  known,  and,  since 
the  transition  from  this  to  the  same  organ  of  birds  and  mammals  may  be 
readily  made,  it  will  be  advisable  to  begin  with  a  close  study  of  the  former. 

Anteriorly  there  enters  into  the  thalamus  from  the  corpus  striatum  of 
the  cerebrum  a  large  bundle:  Tr.  strio-thalamicus.  The  bundle  splits  up  in 
such  a  manner  that  each  one  of  the  ganglia  to  be  named  immediately  re- 
ceives fibers  which,  separated  from  the  others,  pass  to  it  direct.  This  char- 
acterizes all  the  thalamic  ganglia. 

The  nucleus  which  strikes  one  first  is  a  large,  round  one,  composed  of 
immense  multipolar  cells, — the  Nucleus  rotundus  thalami.  It  is  found  like- 
wise in  birds,  here  with  a  retort-shaped,  posteriorly  directed  projection.  In 
fishes,  also,  it  is  a  very  large  ganglion.  In  the  nucleus  rotundus  the  bundles 
of  the  Tr.  strio-thalamicus  split  up  into  fine  rays  (Fig.  81),  and  from  it 
arises  a  fasciculus  which,  passing  backward,  ends  in  the  roof  of  the  mid- 
brain:  Tr.  thalamo-tectalis  (Fig.  83).  The  appearance  of  this  nucleus  and 
its  connections  are  especially  characteristic  and  very  constant. 

Somewhat  anterior  and  dorsal  to  the  Nuc.  rotundus  in  the  neighbor- 
hood of  the  Ggl.  habenulae  lies  the  Nuc.  anterior  (Figs.  70  and  83).  From 
it  arises  a  characteristic  bundle, — characteristic  of  reptiles,  birds,  and  mam- 
mals,— which,  traversing  the  whole  thalamus  quite  parallel  to  the  Tr. 
habenulo-peduncularis,  passes  to  the  base  and  is  lost  in  the  Corpus  mam- 
millare  located  there:  Tr.  thalamo-mammillaris  (Fig.  83), — in  mammals 
called  the  fasciculus  of  Vicq  d'Azyr. 

Ventral  to  the  two  described  nuclei  one  finds  in  reptiles  and  birds, 
probably  also  in  fishes,  in  the  midst  of  the  gray  matter  that  surrounds  the 
median  ventricle,  an  elongated  nucleus  of  large  cells:  Nuc.  magno-cellularis 
strati  grisei.  It  is  probably  fibers  from  it  that  pass  ventrally  to  cross  just 
over  the  infundibulum  as  the  Decussatio  supra-infundibularis.  Besides  this, 
it  probably  sends  bundles  off  posteriorly. 

In  many  reptiles,  especially  turtles,  in  mammals,  and  possibly  in  birds, 
the  two  sides  of  the  ventricular  wall  fuse  together  for  a  little  distance  in 
the  midst  of  the  thalamus.  Thus  arises  the  Commissura  grisea  thalami:  the 
Commissura  mollis  in  mammals.  In  crocodiles,  turtles,  and  snakes  there  lies 
here  a  large  nucleus, — median  nucleus  (Fig.  82), — the  connections  of  whose 
fibers  are  not  yet  clear.  At  any  rate,  it  receives  fibers  from  the  striatum  and 
sends  fibers  out  laterally.  The  median  nucleus  is  not  sharply  defined,  but 
there  lie  in  the  gray  matter  of  the  thalamus,  some  near  to  the  median 


THE    IXTEKBEAIX    OR    THALAMEXCEPHALOX. 


133 


nucleus  and  some  farther  away,  numerous  apparently  similar  cells,  which 
surround  all  of  the  other  more  clearly  defined  nuclei.  I  will  designate  the 
whole  as  the  Nuc.  diffusus  thalami. 

As  was  already  mentioned,  nearly  the  whole  external  surface  of  the 
thalamus  is  covered  hy  the  descending  fibers  of  the  optic  tract.  Between 
the  optic  tract  and  the  two  described  thalamic  ganglia  lies  a  double  gan- 
glion-complex, which  is  very  constant  and  is,  indeed,  to  be  reckoned  in 
with  the  fundamental  ganglia  of  the  opticus  system:  the  Corpus  genic- 
ulatum  laterale  (Figs.  81,  82,  83,  and  84).  It  is  present  in  all  vertebrates. 
In  reptiles  the  author  differentiates  an  antero-ventral  from  a  postero-dorsal 


Tela  chorioid. 
Gangl.  habenulse 

1-3  parts  of  the  Tamia. 

Geniculat.  lat.  dors. 
Nucleus  rotundus 

-  Median  nucleus 

-  Opticus 

i  —  Genie,  lat.  ventr. 

—  Tr.  strio-thal.  dors. 
Sz  .-  Stilus  corp.  genie. 

Tr.  strio-thal.  ventr. 

Nucl.  magno-cell.  strat.  gris 
Basal  optic  root 


Fig.  82. — Frontal  section  through  the  Thalamus  opticus  of  a  young  alligator. 


portion  (see  Fig.  82).  It  is  possible  that  the  latter  merges  into  what  in 
man  is  called  the  Corpus  geniculatum  mediale.  At  least  an  analogously 
located  line  may  be  seen  in  birds  arising  from  the  Decussatio  transversa 
and  which  may,  in  mammals,  be  followed  as  far  as  to  and  into  the  Gen- 
iculatum mediale.  There  arises  from  the  Corpus  geniculatum  laterale — 
probably  also  from  the  Corp.  genie,  med. — a  posteriorly  directed  Stilus 
corp.  geniculati,  which  is  lost  in  the  posterior  portion  of  the  midbrain-roof, 
possibly  communicating,  on  the  way,  with  the  nucleus  prstectalis,  later  to 
be  described.  In  birds  with  enormously  developed  geniculatum  it  is  very 
large. 


134  ANATOMY    OF    THE    CENTEAL    NEEYOUS    SYSTEM. 

In  the  geniculatum  a  part  of  the  optic  nerve  ends  in  striking  ramifica- 
tions in  whose  midst  are  the  dendrites  of  elongated  fusiform  cells  whose 
median  end  ramifies  within  a  bundle  which  probably,  also,  belongs  to  the 
optic  system.  These  structures  are  well  represented  in  Fig.  81. 

In  the  midst  of  all  these  ganglia  end  the  Tr.  thalamo-bulbares  et  spinales. 
It  is,  however,  still  impossible  to  designate  just  what  nucleus  is  the  terminal 
one  (see  Fig.  64,  Rad.  Thai.}. 

With  the  mention  of  the  Nuc.  entopeduncularis,  a  group  of  large  gan- 
glion-cells median  to  the  Tr.  strio-thalamici,  I  have  enumerated  the  most 
important  ganglia  characteristic  of  the  thalamencephalon  of  lower  verte- 
brates. 

Fig.  83  shows  a  schematic  representation  of  the  nuclei  of  the  thalamus 


Fig.  83. — Schema  of  the  principal  nuclei  and  tracts  of  the  interbrain  of  the  pigeon. 

in  the  pigeon.     It  gives  a  good  general  idea  of  the  structural  relations 
already  quite  complicated  in  birds  and  as  yet  not  well  known. 

What  is  recognized  as  common  to  the  nuclei  of  the  thalamus  in  all 
lower  vertebrates  may  be  thus  summarized:  The  nuclei  of  the  interbrain 
receive  fibers  from  the  basal  ganglia  of  the  forebrain,  and  give  off  posteriorly 
new  tracts  to  centers  which  lie  at  a  lower  level.  Furthermore  they  are  joined 
to  the  ganglia  of  the  hypothalamus  in  manifold  combinations.  The  fibers 
which  pass  to  the  roof  of  the  midbrain  and  to  the  medulla  and  spinal  cord 
have  already  been  mentioned.  We  will  soon  find  that  also  from  the  nuclei 
of  the  hypothalamus  tracts  lead  to  the  cerebellum  and  to  other  regions  of 
the  midbrain  than  to  the  roof.  So  we  see  in  the  thalamencephalon  a  great 


THE    IXTERBRAIX    OR   THALA1IEXCEPHALOX. 


135 


center  which  is  inserted  in  between  an  important  part  of  the  cerebrum  and 
nearly  all  other  parts  of  the  brain. 

Traces  of  a  progressive  development  of  the  thalamus  are  found  in  the 
reptiles,  where  from  the  frontal  cerebral  cortex  a  bundle  arises  which,  end- 
ing in  the  thalamus,  represents  a  direct  cortico-thalamic  tract.  In  birds 
the  same  thing  is  even  more  evident,  and  one  may  recognize  how,  with  the 
development  of  an  extended  cerebral  cortex,  more  and  more  bundles  appear 


Tr.  occipito-tectalig     _1 
Commis.  ant.    ... 

Tr.  strio-thal.  inedialis 


Tr.  strio-thal.  lat. 
Tr.  septo-mesence- 1 
phalicusj 
Nucleus  rotundusl     "*' 

thalami/    --. — 

Median  options  bun-) 

die  to  the    ganglion}- 

istlin.ij 

Fartes  corp.  genie,  lat. 

£j 

.clesj 

Tr.  tegmento 

cerebellnris 

Corpus  resti  forme 

Fillet  — 

Tr.  thalamo-tcctalis   — 
N.  oculo-mot 


Fig.  84. — Sagittal  section  through  the  Thalamus  opticus  of  the  domestic 
pigeon.    Hsematoxylin  staining. 


which  pass  from  it  into  the  ganglia  of  the  thalamus.  In  mammals  these 
Tr.  cortico-thalamici  have  undergone  such  a  great  development  that  they 
make  the  greatest  system  of  the  thalamencephalon,  and  taken  together  are 
designated  Corona  radiata  of  the  Thalamus.  With  this  transformation  there 
goes  hand  in  hand  a  gradual  enlargement  of  the  ganglia;  so  that  it  is  no 
longer  possible  to  recognize  the  comparatively  simple  relations  which  exist 
in  reptilia  and  to  homologize  with  certainty  the  large  thalamic  nuclei  of 


136  ANATOMY    OF    THE    CENTRAL    NERVOUS    SYSTEM. 

mammals  with  the  previously  described  nuclei  of  reptilia.  It  will  require 
much  work  yet  before  it  is  known  what  new  structures  have  been  introduced 
and  what  is  to  be  attributed  only  to  the  increase  of  structures  already  pres- 
ent. As  yet,  it  is  not  possible  to  determine  more  than  that,  in  mammals,  fibers 
from  the  Tr.  strio-thalamici  end  in  all  or  nearly  all  of  the  thalamic  ganglia, 
and  that  the  Tr.  thalamo-'bulbares  et  spinales  are  developed  from  one  of  the 
ventral  nuclei. 

Only  a  few  thalamic  nuclei  of  mammals  may  be  homologized  with  those 
of  lower  vertebrates;  and  these  will  be  more  minutely  described,  because, 
in  them,  we  have  learned  to  recognize  the  whole  process  of  the  addition  to 
already  existing  systems  of  cerebral  tracts  which  are  not  necessary  to  the 
existence  of  lower  vertebrates.  First,  there  is  the  Corp.  geniculatum.  In 
all  animals  fibers  from  the  the  optic  nerve  pass  into  it.  From  birds  upward 
in  the  vertebrate  series  there  is  formed  a  tract  from  the  cerebral  cortex  to 
the  optic  center.  Whether  in  birds  it  reaches  the  geniculatum  is  not 
known,  but  that  it  does  so  in  mammals  has  been  conclusively  demonstrated. 
So  you  see,  anatomically  recognizable,  how  the  primitive  terminal  center 
of  the  optic  nerve  passes,  in  higher  animals,  into  relations  with  tracts  which 
arise  in  the  organ  of  thought,  of  memory,  of  association,  etc. 

For  the  ventral  nucleus  in  wiiich  the  tracts  to  the  medulla  and  spinal 
cord  end,  a  similar  relation  has  also  been  recognized  in  the  mammals.  Here 
it  receives  afferent  bundles  from  the  cerebral  cortex,  indeed,  from  psycho- 
motor  areas:  from  cortical  areas  whose  loss  diminishes  the  ability  to  carry 
out  acquired  movements  or  movements  which  are  the  result  of  associative 
reflexes. 

Though  these  nuclei  exist  in  lower  vertebrates,  it  is  only  in  the  highest 
of  the  series  that  the  cerebral  tracts  are  added. 

So  much  for  the  ganglia  peculiar  to  the  thalamus.  There  still  remains 
for  consideration  a  narrow  region  that  is  usually  reckoned  in  with  it:  the 
boundary  region  between  the  interbrain  and  the  midbrain,the  metathala- 
mus. 

Just  anterior  to  the  roof  of  the  midbrain  and  continuous  with  it,  simply 
extending  out  into  the  thalamus  anteriorly,  we  find  the  Nuc.  prcetectalis. 

It  has  not  been  demonstrated  yet  in  mammals,  though  I  believe  that 
it  is  to  be  recognized  in  the  most  anterior  portion  of  the  ganglion  reckoned 
until  now  as  belonging  to  the  gray  matter  of  the  anterior  quadrigeminal 
body.  Of  this  nucleus  something  has  been  said  before  (Figs.  71  and  72), 
and  also  of  the  fact  that  in  it  probably  bundles  from  the  stilus  of  the  gen- 
iculatum end  (Fig.  83).  Median  from  it  lies  a  not  very  sharply  defined 
nucleus,  from  which  the  bundles  of  the  commissura  posterior — Nuc.  com- 
missura  posterioris — appear  to  develop,  and  ventral  to  it  one  finds,  through- 
out the  whole  vertebrate  series,  the  nucleus  of  origin  of  the  posterior  longi- 


THE    IXTERBRAIX    OR    THALAMEXCEPHALOX. 


137 


tudinal  bundle  (Fig.  44):  an  elongated,  perpendicularly  placed  nucleus 
which  lies  near  the  median  line,  one  on  each  side.  From  it  develop  the  most 
anterior  fibers  of  the  Fasciculus  longitudinalis  posterior,  the  bundle  which 
we  have  repeatedly  met  from  the  spinal  cord  on  to  the  interbrain.  That  it 
later  receives  bundles  from  the  nuclei  of  the  cerebral  nerves  has  already  been 
mentioned. 

The  nucleus  of  the  posterior  longitudinal  fasciculus  lies  rather  far 
ventral,  and  might,  in  fact,  be  reckoned  with  the  hypothalamus  instead  of 
the  metathalamus.  In  fishes  it  certainly  belongs  to  the  former. 

Lateral  from  it — i.e.,  in  the  postero-lateral  portion  of  the  thalamus — 
lies  the  nucleus  ruber  tegmenti:  a  usually  well-defined  nuclear  mass  from 
which  fibers  arise  which  decussate  soon  after  their  origin,  pass  dorsally,  and 


Fig.  85. — Frontal  sections  through  the  boundary  between  the  base  of  the 
midbrain  and  lobi  inferiores.  From  the  teleost:  Zoarces  viviparus.  (A  young 
specimen  three  centimeters  long.)  a,  Nucleus  rotundus  thalami.  ft,  Supplemen- 
tary nuclei  of  the  same,  c,  Post,  ganglion  of  inferior  lobe,  e,  Infundibulum.-  f, 
Tr.  lobo-cerebellaris  frontalis.  g,  Tr.  lobo-cerebellaris  caudalis.  h,  Fritsch's  com- 
missure, i,  Ggl.  profundum  mesencephalici  lat.  k,  Ggl.  lat.  mesencephalici  Torus 
semic.  I,  Valvula  cerebelli.  m,  m',  n,  Single  portions  of  the  fiber-bundles  from  the 
roof  (see  also  Fig.  67).  o,  Nucl.  N.  Oculomot.  and  Fasciculus  longitudinalis 
post,  p,  Commissura  post. 


end  in  the  cerebellum.  These  bundles  are  comprehended  under  the  term 
Tractus  tegmento-cerebellaris:  the  anterior  peduncle  of  the  cerebellum.  For 
the  nucleus  see  Fig.  83;  for  the  tract  see  Figs.  71  and  84,  and  for  the 
decussation  see  Figs.  65,  83,  and  84. 

"We  turn  our  attention1  now  to  the  structure  at  the  base  of  the  inter- 


Seven  pages  of  the  original  (131  to  137)  are  here  briefly  summarized. 


138 


ANATOMY    OF   THE    CENTRAL   NERVOUS    SYSTEM. 


brain, — to  the  hypothalamus, —  depending  largely  upon  the  figures  for  our 
medium  of  expression. 

Of  the  many  decussations  in  the  base  of  the  interbrain  the  most  im- 
portant is  that  of  the  tractus  optici:  the  chiasma. 

Just  behind  the  chiasma,  and  very  closely  associated  with  it,  lie  the 
tracts  from  the  Ganglion  ectomamillare  (Fig.  87),  which  together  form  the 
Commissura  post-chiasmatica. 

Somewhat  dorsal  to  them  we  find  the  bundles  of  the  Decussatio  trans- 
versa,  or  Gudden's  commissure  (see  Fig.  89).  They  arise  from  the  most  pos- 
terior portion  of  the  midbrain,  possibly  from  the  Ggl.  isthmi,  which  lies 
close  under  the  cerebellum  (Fig.  88). 

Farther  dorsal  lies  a  large-fibered  decussation  whose  constituents  de- 


Fig.  86.— Sagittal  section  of  brain  of  barbel:    Barbus  fluviat. 


scend  from  the  gray  matter  of  the  central  cavity  of  the  third  ventricle:  the 
Decussatio  supra-infundibulus.  In  the  brain  of  the  selachians  and  amphib- 
ians it  is  easy  to  get  the  greater  part  of  the  Decussatio  transversa  in  a  single 
section,  as  shown  in  Fig.  89. 

From  the  somewhat  uninspiring  picture  which  the  present  condition  of 
our  knowledge  of  the  hypothalamus  of  the  lower  vertebrates  yields  let  us 
turn  to  a  more  encouraging  one. 

To  the  few  really  well-known  tracts  in  the  brain  belongs  that  one 
which  serves  the  function  of  vision.  The  optic  nerve  has  already  been  men- 
tioned incident  to  the  description  of  the  roof  of  the  midbrain;  but,  since 
we  find  all  of  its  fibers  united  just  anterior  to  the  hypothalamus,  it  will  be 
profitable  to  view  the  whole  tract  together. 


THE    INTEBBBAIN    OE   THALAMENCEPHALON. 


139 


We  know  at  present  that  parts  of  the  optic  nerve  arise  from  the  large 
ganglion-cells  of  the  retina  (S.  E.  y  Cajal,  Monakow),  and  we  know  that  an- 
other part  passes  from  the  roof  of  the  midbrain  itself  to  be  distributed  in 
the  retina.  The  retina  itself  may  be  looked  upon  as  a  system  of  neurons 
arranged  in  strata  one  above  the  other.  A  part  of  these  neurons  stand  in 
direct  relation  to  the  Opticus,  as  just  stated;  while  a  part  are  connected 
with  other  cells,  of  the  second,  third,  and  fourth  orders,  propagating  the 
stimulus  received  by  the  peripheral  neurons  of  the  first  order.  In  the  midst 


Dec.  post-chiasmatica 

•  Dec.  transversa 
Basal  options  root 

•  Tr.  strio-thalam. 

•  Dec.  supra-infundibularis 


i«H Ggl.  ectomamillar 


N.  ocnlo-motorius 
Tr.  quinto-thalamicus 


—    Fasc.  longit.  post. 


—  N.  trigeminus 


Fig.  87. — Horizontal  section  through  the  hypothalamus,  chiasma,  and 
medulla  of  a  lizard. 


lie  many  cells  the  distribution  of  whose  processes  make  it  evident  that  they 
connect  one  part  of  the  retina  to  another.1 

From  the  eyeball  the  optic  nerve  passes  into  the  cranial  cavity.  In 
fishes  whose  eyes  are  relatively  much  larger  than  man's,  also  in  birds,  the 
nerves  in  question  are  enormous,  and  in  brain-sections  of  these  animals 
dominate  the  field.  At  the  base  of  the  skull  they  cross  in  the  chiasma, 
which  lies,  as  above  stated,  just  anterior  to  the  hypothalamus.  This  decus- 
sation  is,  in  most  animals,  complete,  but  in  some  birds  and  probably  in  the 


1  For  a  more  exact  description  see  S.  R.  y  Cajal's  monograph  on  "The  Retina." 
There  is  a  German  translation  bv  Dr.  Greef. 


140 


ANATOMY    OF   THE    CENTRAL   NERVOUS    SYSTEM. 


majority  of  mammals  the  decussation  is  only  partial.     That  probably  de- 
pends upon  the  position  of  the  eyes  which,  in  the  lateral  position,  as  in 


Fig.  88. — Sagittal  section  some  distance  from  the  median  line  of  the  brain 
of  Varanus  griseus,  showing  the  course  of  the  Decussatio  transversa  from  the 
chiasma  to  its  terminus. 

fishes,  reptiles,  etc.,  have  no  part  of  the  field  of  vision  in  common,  while, 
in  the  position  found  in  the  owls,  the  ape,  and  man,  the  visual  field  is  quite 


ncephal. 


/  Decussation  of  the  deep  medul- 
i     latedf 


—  Tr.  strio-thalam. 
Decuss.  transversa 


Fig.  89. — Frontal  section  through  the  midbrain  of  Scyllium  canicula. 

separate  only  in  the  lateral  portions,  the  images  of  the  median  portion  being 
coincident.     So  it  is  explained  why  careful  investigations  on  the  chiasma 


THE    IXTEBBBAIX    OR    THALAMENCEPHALON. 


141 


have  led  to  very  contradictory  results  over  the  decussation,  according  to  the 
animal  which  the  investigator  has  studied.     Possibly  the  conditions  vary 


Cbiasma 

Dec.  of  tract,  pallii. 

Dec.  tr.iusrersa 


Peduncle  of  the  decussatio 
supra-mfundibularig 


Fig.  90. — Horizontal  section  through  the  thalamus  of  an  adult  shark: 
the  Scyllium  canicula. 


Ggl.  of  the  central  gray  matter    . 

Decuss.  tnberis.— '-.. 

Tr.  strio-thalam.  ad  lob.  inf. — 

Decuss.  supra-infundibularis 


Tr.  strio-thalam 

Supplementary  Ggl.  to  nuc.  rotundus 

Nucl.  rotnndus 

Peduncle  of  Fritsch's  commissure  — 

Tr.  lobo-cerebellares • 


Comm.  ansnl. 

Tr.  tecto-bulb.  et  spin.  cruc. 
Terminal  nucleus  of  the  Trijrem. 


Fig.  91. — Horizontal  section  through  the  thalamus  of  a  teleost: 
GoUo  fluviatilis. 


even  for  different  individuals  of  the  same  species.     We  are  quite  certain 
of  the  partial  decussation  in  mammals,  especially  man,  where  degenerations 


142 


ANATOMY   OF    THE    CENTRAL   NERVOUS    SYSTEM. 


in  the  optic  nerve  after  loss  of  the  eyes  could  be  compared  with  the  visual 
images  received  during  life. 

The  decussation  is  not,  however,  so  simple  as  represented  in  Figs.  87 
and  89.  The  bundles  are  plaited  together  more  or  less,  in  fishes  one  nerve 
passing  through  a  slit  in  the  other. 


Tela  chorioid. 
Tr.  strio-thalam. 


....---    Tr.  options 


.  Decns.  Tr.  tegmento-cerebelL 
.  Dec.  bypoth.  sup. 

Genicul.  lat. 
,  N.  ocnlo-mot. 
.  Tr.  teoto-bulb.  et  spin. 


..J— — -  Comm.  iin.-ul. 


Fig.  92. — Horizontal  section  through  the  brain  of  the  Scyllium  canicula  to  sho\ 
the   decussations   in   the  base   of  the  brain. 


Beyond  the  chiasma  the  reunited  fasciculi  pass  backward  and  up- 
ward (Fig.  88),  inclose  the  thalamus,  sending  into  the  externally  located 
Corpus  geniculatum  a  large  portion  of  the  collaterals  from  the  fibers  (com- 


THE    INTERBBAIN    OR   THALAMEXCEPHALON.  143 

pare  Figs.  81  and  82).  The  tract  thus  becomes  little  poorer  in  fibers. 
Splitting  up  into  numerous  branches  it  now  passes  to  the  roof  of  the  mid- 
brain,  where  it  is  already  familiar  to  you.  These  tracts  ascending  to  the 
corpora  quadrigemina  might  be  called  the  peduncles  of  the  quadrigemina, 
as  they  have  been  in  mammals,  but  it  is  preferable  to  retain  the  term 
"roots"  because  these  tracts  contain  in  mammals  also  fibers  from  the  cere- 
brum. 

In  Fig.  66  one  sees  a  part  of  the  ends  of  the  optic  fibers.  One  may 
note  here  that  they  stand  in  close  relation  to  those  tracts  which  arise  in 
the  deep  medullated  stratum  of  the  midbrain.  Not  only  do  the  dendrites 
of  these  cells  from  which  arise  the  bundles  to  the  sensory  nuclei  of  the 
medulla  and  spinal  cord  dip  into  the  midst  of  the  optic  system,  but  bundles 


Comm.  habenul.  p.  front. 
—  Fas.  Tr.  habenulo-pedun 

~  Opticus 

Tr.  strio-thalam. 


~    --i Decuss.  transversa 

Dec.  Tr.  pallii 


Fig.  93. — Cross-section  through  anterior  portion  of  thalamus  of  Scyllium  canicula. 


of  axis-cylinders  pass  into  the  optic  layer  from  the  sensory  fiber-system  above 
mentioned. 

In  mammals  a  majority  of  the  fibers  of  the  optic  end  in  the  Geniculatum 
laterale  and  the  remainder  in  the  Tectum  mesencephali. 

We  will  not  leave  the  consideration  of  the  Thalamencephalon  without 
impressing  the  fact  that  this  segment  of  the  brain,  in  lower  vertebrates  at 
any  rate,  is  joined  to  the  cerebrum  by  relatively  small  tracts.  I,  therefore, 
present  at  the  close  of  this  chapter  a  section  from  the  most  anterior  portion 
of  the  interbrain  of  the  Scyllium  canicula  just  behind  the  Ggl.  habenulae. 

Note  that  nearly  the  whole  section  is  filled  with  the  opticus  and  with 
the  commissures  associated  with  the  optic  system;  also  a  few  which  cor- 
respond to  the  system  of  the  ganglion  habenulae.  Note  that  to  the  cerebrum 


144  ANATOMY    OF    THE    CENTRAL    NERVOUS    SYSTEM. 

the  somewhat  ventral  bundles  of  the  Tr.  strio-thalamici  pass  out.  When 
the  cerebral  cortex  becomes  prominent,  as  in  the  higher  animals,  this  tract 
is  associated  with  those  which  pass  from  the  cortex  into  the  thalamus  and 
also  those  which  pass  through  and  beyond  the  thalamus.  But  even  up  to 
mammals  in  the  vertebrate  series  one  can  differentiate  from  the  great  fiber- 
systems, — the  Capsula  interna, — severed  at  this  point,  the  bundle  to  the 
striatum:  the  Tr.  strio-thalamicus.  But  in  mammals  they  play  a  subor- 
dinate role  as  far  as  size  indicates. 


CHAPTEE    XI. 
THE     CEREBRUM  :    THE  PROSENCEPHALON. 

FROM  those  brain-segments  already  considered  in  different  classes  of 
vertebrates  very  varied  direct  tracts  pass  into  the  anterior  segment:  the 
cerebrum.  In  frogs  the  interbrain  only  is  connected  with  it;  in  other 
vertebrates  the  midbrain  also,  and,  finally,  in  mammals  it  receives  a  con- 
nection with  the  spinal  cord,  whose  centers  are,  in  other  animals,  much  more 
independent  of  it.  A  direct  tract  from  cerebrum  to  cerebellum  is  not 
known,  but  even  here  there  is,  in  mammals,  a  possible  connection  through 
the  tegmental  nucleus  and  through  the  frontal  ganglia.  The  influence  which 
the  cerebrum  must  exert  over  the  lower  centers  direct  is  in  varying  strength 
according  to  the  vertebrate  class.  This  fact,  so  evident  to  the  comparative 
anatomist,  remained,  curiously  enough,  up  to  the  present  quite  ignored  in 
the  interpretation  of  physiological  and  psychological  phenomena. 

It  is  important,  naturally,  to  designate  which  part  of  the  cerebrum  is 
connected  with  other  parts  of  the  brain.  You  will  see  at  once  that  especially 
important  tracts,  those  from  the  cortex,  appear  relatively  late  in  the  series, 
and  much  later  still  do  they  reach  comparative  perfection;  indeed,  it  is 
only  in  mammals  that  such  tracts  pass  to  most  of  the  other  parts  of  the 
brain. 

We  can  imagine  a  schematic  cerebrum.  Picture  to  yourself  the  ovoid 
vesicle  which  evaginates  from  the  common  ventricle  near  the  terminal 
lamina  on  either  side.  It  increases  in  thickness  at  the  base,  forming  there 
a  large  body:  the  Corpus  striatum.  In  the  floor  of  the  vesicle  end  the  olfac- 
tory nerve-fibers,  and  we  may  at  once  differentiate  the  olfactory  apparatus 
from  the  corpus  striatum.  Thus  we  have  a  second — indeed,  characteristic 
— division  of  the  cerebrum, — sometimes,  in  fact,  given  the  dignity  of  a  po- 
sition co-ordinate  with  the  brain-segments,  and  called  the  Khinencephalon. 
The  portion  which  remains  of  the  vesicle — namely,  the  roof  and  sides — is 
called  the  Pallium,  or  Mantle. 

The  mantle  may  consist  of  (1)  a  simple  epithelial  plate,  as  in  teleosts; 

(2)  the  lateral  portions  may  thicken  into  nerve-areas,  as  in  cyclostomes; 

(3)  lateral  walls  and  anterior  walls  may  be  thickened,  as  in  selachians,  or, 
finally  (4)  nearly  the  complete  mantle  may  be  transformed  into  brain-sub- 
stance, only  the  most  posterior  part  retaining  its  epithelial  character  and 
persisting  as  the  Tela  chorioidea.    Thus  is  constructed  the  brain-mantle  in 

(145) 


146  ANATOMY    OF   THE    CENTRAL    NERVOUS    SYSTEM. 

amphibians  and  reptiles,  in  birds  and  mammals.  The  development  of  the 
mantle  is  of  especial  interest.  From  a  small  beginning  in  teleosts  it  develops 
into  the  enormous  organ  which  we  recognize  in  man  as  the  cerebral  hemi- 
spheres, and  with  this  development  progresses  the  capacity  for  the  higher 
psychical  activities. 

Fig.  20  shows  well  the  separate  parts  of  the  embryonic  human  brain, 
which  may  serve  here  as  a  prototype,  since  in  the  depicted  one  only  struct- 
ures appear  which  are  constant  in  their  recurrence.  Study,  also,  Fig.  55, 
and  note  the  varying  development  of  the  mantle  shown  in  the  four  sagittal 
sections  given. 

I.    THE    OLFACTORY   APPARATUS   AND   THE    CORPUS    STRIATUM. 

These  structures,  together  with  the  spinal  cord,  cerebellum,  and  mid- 
brain,  show,  through  the  whole  series,  little  essential  difference. 

Except  the  Ggl.  habenulae  and  optic  system,  no  other  portion  of  the 
brain  is  so  constant  in  structure  as  the  olfactory  apparatus.  Only  the  rela- 
tive size  varies;  the  structural  features  remain  unchanged.  For  our  knowl- 
edge of  the  structure  we  are  especially  indebted  to  S.  E.  y  Cajal,  Van 
Gehuchten,  Kolliker  (and  Edinger). 

From  the  epithelium  of  the  nasal  mucous  membrane  (Fig.  16,  a)  long 
terminal  fibrilla?  run  backward.  They  are  called  Fila  olfactoria,  and  pass 
through  the  cribriform  plate  into  the  cranial  cavity. 

Within  the  cranium  they  reach,  after  a  longer  or  shorter  course  (accord- 
ing to  the  class),  the  anterior  end  of  the  brain,  where  they  enter  within  it. 
The  whole  bundle,  which  may  be  subdivided,  is  called  the  Nervus  olfac- 
torius.1 

The  Fila  olfactoria  pass  to  an  anteriorly  directed  evagination  of  the 
forebrain-vesicle.  This  evagination  forms  on  the  base  of  the  brain  a  more 
or  less  elongated  tube  which,  in  most  animals,  remains  hollow.  This  tube 
is  called  Lobus  olfactorius  anterior.  From  the  place  where  it  passes  into  the 
base  of  the  brain  begins  the  posterior  olfactory  region,  which  in  mammals 
is  called  the  Lobus  olfactorius  posterior.  Since  in  lower  vertebrates  the 
homology  is  not  yet  certain,  we  will  designate  the  anterior  simply  as  Lobus 
olfactorius,  and  the  posterior,  which  includes  the  whole  base  of  the  brain, 
as  area  olfactoria. 

At  the  place  where  the  Fila  olfactoria  enter  the  anterior  end  of  the 
olfactory  lobe  they  break  up,  sometimes,  after  decussation  and  exchange  of 
fibers,  into  very  fine  terminal  ramifications.  These  enter  the  apex  of  the 
lobe,  where  they  meet  the  terminal  ramifications  of  cells  which  lie  in  that 


1  The  term  Radix  olfactoria  would  be  a  better  one,  since  Figs.  15  and  16  show 
the  Fila  olfactoria  and  the  "olfactory  nerve"  to  be  homologous  to  the  roots  of  the 
spinal  and  of  most  of  the  cranial  nerves,  being  the  neuraxons  of  the  neurons  involved. 


THE  CEREBRUM  OR  PROSEXCEPHALON. 


147 


region.  Thus  the  fine  ramification  of  the  olfactory  neuron  of  the  I  order 
comes  into  close  relation  with  the  dendrites  of  cells  which  represent  the 
olfactory  neuron  of  the  II  order. 

The  united  terminal  ramifications  are  to  be  seen,  even  with  low  power, 
on  all  sections  through  the  apex  of  the  lobe  as  spherical  structures  located 
just  beneath  the  fibers  of  the  olfactory  nerve:  Glomeruli  olfactorii.  From 
the  olfactory  cells  of  the  II  order  arise  new  neuraxons,  and  these  pass  back- 
ward toward  the  area  olfactoria. 

The  entering  and  freely  decussating  Fila  olfactoria,  the  dendrites  of 
the  olfactory  cells  (II  order),  and  the  glomeruli  together  make,  at  the  apex 
of  the  lobe,  a*  characteristic  picture,  which  is  called  Formatio  bulbaris. 

In  most  animals  it  makes  a  swelling  anteriorly,  which  is  called  the 


Fig.  94. — Sagittal  section  through  the  Bulbus  olfactorius  of  a  frog. 
(After  P.  R.  y  Cajal.) 

Bulbus  olfactorius.  Sometimes,  however,  the  apex  of  the  lobe  is  overlaid 
with  the  Formatio  bulbaris  farther  back  than  the  visible  bulb  reaches. 
Certain  amphibians  and  reptiles  especially  show  a  second  ovoid  bulbar  for- 
mation on  the  median  side  of  the  lobe  somewhat  back  of  the  usual  position. 
Emerging  from  the  posterior  and  lateral  pole  of  the  spheroidal  bulb 
one  always  sees  the  olfactory  tract  of  the  II  order, — Tractus  olfactorius, — 
which,  at  first,  covers  the  olfactory  lobe,  but  later  collects  in  one  or  more 
bundles  at  its  outer  side  and  passes  posteriorly.  This  second  olfactory 
bundle  is  so  large  that  with  the  unaided  eye  it  may  usually  be  seen  as  a  white 
bundle.  In  several  teleosts  the  olfactory  bulb  is  very  large  and  located  far 
forward  in  the  skull.  Thence  the  tracts  pass  as  two  great  white  fasciculi 
on  either  side  backward  into  the  brain.  They  might  easily  be  mistaken  for 


148 


ANATOMY    OF   THE    CENTRAL    NERVOUS    SYSTEM. 


the  olfactory  nerve,  which,  however,  terminated  at  the  inconspicuous  olfac- 
tory lobe,  and  the  part  of  the  olfactory  apparatus  which  passes  from  the 
lobe  to  the  brain — to  the  Lobus  olfactorius  posterior — must  be  designated 
the  olfactory  tract. 


Fig.  95. — Brain  of  the  barbel:    Barbus  fluviatilis.     (Sagittal  section 
near  the  median  line.) 


In  the  brain  of  the  barbel  (Fig.  95)  one  sees  the  long  course  of  the  tract, 
also  the  entrance  of  the  fila  into  the  bulbus,  which  lies  far  anterior  to  the 
rest  of  the  brain.  In  the  perch,  however,  the  bulbus  is  so  close  to  the  brain 
that  the  olfactory  tract  (Bad.  olf.)  is  very  short. 


Fig.  96. — Brain  of  Perca  fluviatilis.     Olfactory  apparatus  and  corpus  striatum 
only  shown.      (Sagittal  section  somewhat  lateral.) 


The  posterior  end  of  the  secondary  olfactory  fibers  was  long  unknown 
until  C.  L.  Herrick  was  able  to  show  that  one  part  ends  in  the  basal  portion 
of  the  Lobus  olfactorius  posterior,  and  another  part  farther  dorsal  in  a  part 
of  the  brain  which  lies  upon  the  corpus  striatum.  The  author  has  carefully 


THE  CEKEBKUM  OR  PBOSENCEPHALON. 


149 


studied  the  relations  in  fishes  and  reptiles  and  has  determined  that,  in  the 
recurrence  of  the  same  relation  in  animals  so  far  remote  from  each  other  in 
the  series,  we  have  to  do  with  a  fundamental  principle.  This  newly  out- 
lined portion  of  the  brain,  which  always  lies  close  to  the  corpus  striatum,  I 
have  designated  the  Epistriatum. 

The  Epistriatum  is  most  sharply  denned  in  the  reptilian  brain  (see  Fig. 
97),  where  it  is  also  differentiated  in  its  minute  structure  (compare  also 
Fig.  118). 

In  amphibia  the  fibers  of  the  olfactory  tract  are,  for  the  most  part,  non- 
medullated,  and  in  birds  very  sparingly  so,  since  these  animals  have  a 
somewhat  atrophic  olfactory  apparatus.  Hence  it  has  not  been  possible  to 
demonstrate,  in  both,  the  course  of  the  fibers  in  question  or  the  location  of 


Fig.  97. — Brain  of  the  lizard  (Varanus),  showing  the  course  of  the  median 
fibers  from  Bulbus  olfactorius  and  the  Epistriatum.  Lob.  olf.  post.,  with  its 
fibers,  not  shown. 


the  Ggl.  epistriaticum.  In  mammals  the  tract  from  the  bulb  is  well  known. 
One  sees  it  pass  backward  on  the  base  of  the  brain,  and  recognizes  that 
bundles  pass  continuously  from  it  into  the  Lobus  olfactorius  posterior, 
possibly  into  the  cortex  of  the  Lobus  olfactorius  anterior.  The  posterior 
end  has,  as  yet,  not  been  with  certainty  located.  It  is  possible  that  the 
structure  known  as  Nuc.  amygdalae  corresponds  to  the  Epistriatum  of  the 
lower  vertebrates. 

The  median  portion  of  the  secondary  olfactory  tract  ends,  then,  in  the 
Epistriatum,  while  the  lateral  portion  ends  farther  ventral  in  the  Lobus 
olfactorius  posterior. 

Even  in  the  teleosts — the  carp,  for  example — one  sees  that,  lateral  to 
the  large  bundles  en  route  to  the  epistriatum — viz.,  the  median  fasciculus — 
smaller  bundles  pass  into  the  area  olfactoria.  This  lateral  olfactory  fascicu- 


150 


AXATOJIY    OF    THE    CEXTRAL    NERVOUS    SYSTEM. 


lus  disappears  in  the  midst  of  the  Lobus  olfactorius  posterior,  which,  more- 
over, is  not,  by  superficial  examination,  to  be  differentiated  from  the  stri- 
atmn,  whose  ventral  portion  it  forms. 

The  olfactory  apparatus  of  amphibia  has  not  yet  been  thoroughly 
studied,  but  in  reptiles  and  in  mammals  one  can  readily  recognize  that 
many  fibers  pass  into  the  base  of  the  brain,  into  the  Lobus  olfactorius  pos- 


Commissura  habeuularis 


Fig.  98. — Schema  of  a  horizontal  section  through  the  brain  of  Cyprinus 
carpio,  showing  subdivisions  of  the  corpus  striatum ;  also  the  course  of  the  olfac- 
tory fiber-system. 


terior;  also  that  fibers  disappear  in  the  Lobus  olfactorius  anterior.  They 
plunge  in,  to  break  up  into  fine  terminal  ramifications  and  come  into  rela- 
tion with  the  dendrites  of  the  large  cells, — here  called  cortex-pyramids. 
Corresponding  with  this  distribution,  we  had  to  assume  two  classes  of  fibers: 
the  Tr.  bulbo-epistriatici  and  the  Tr.  bulbo-corticales;  in  the  last-named 
tract  were  differentiated  fibers  for  the  anterior,  and  fibers  for  the  posterior 
portion  of  the  olfactory  lobes.  Finally  a  connection  probably  also  exists, 


THE    CEREBRUM    OR    PROSEXCEPHALOX. 


151 


at  least  in  large  reptiles,  between  the  cortex  of  the  olfactory  lobes  and  the 
epistriatum:    Tr.  cortico-epistriaticus. 

The  olfactory  apparatus,  then,  as  far  as  described,  consists  of  a  com- 
bination of  at  least  two  neurons:  a  peripheral  neuron  of  the  I  order,  from 
the  nasal  mucous  membrane  to  the  bulbus;  and  a  central  neuron  of  the 
II  order,  from  the  bulbus  to  one  of  the  several  termini  above  enumerated. 
But  from  these  terminations  proceed  other  tracts  of  the  third,  or  higher, 
order.  In  the  first  place,  the  olfactory  centers — i.e.,  the  terminations  of  the 
II  neuron  are  uniformly  connected  by  a  tract  with  the  Epithalamus,  espe- 
cially with  the  Ggl.  habenulae.  Carefully  study  these  relations  in  Fig.  98. 


Epistriatum 


Segio  part.  caud.  s trial. 

Tsenia  with  tl.ree  origins  of  bundles 

Nucleus    t;..'liiy 


Tr.  strio-tlmlamicus 


Tr.  septo-mesenceph. 
Decuss.  transverse 


Fig.  99. — Frontal  section  through  the  most  posterior  portion  of  the  Cere- 
brum of  the  Swamp-turtle:  Emys  lutaria.  Note  dorsally  the  mantle  with  its 
cortex,  ventrally  the  transition  to  the  thalamus  with  the  underlying  chiasma, 
at  the  right  the  posterior  end  of  the  olfactory  region. 


A  second  connection  passes  from  the  olfactory  center  to  the  brain- 
cortex.  This  tract  might  be  designated  the  Tr.  cortico-olf actor ii.  It  is 
absent  in  fishes,  is  probably  present  in  amphibians  and  birds,  and  is  well 
developed  in  reptiles  and  mammals. 

The  cortico-olfactory  tract  is,  as  you  will  find  later,  the  first  connection 
which  was  established  between  the  brain-cortex  and  any  sensory  apparatus. 
Just  because  of  this  important  fact  this  tract  will  be  discussed  later  in 
connection  with  the  development  of  the  brain-mantle. 


152 


ANATOMY    OF   THE    CENTRAL   NERVOUS    SYSTEM. 


The  cortical  center  of  the  olfactory  apparatus  reaches  in  mammals  its 
highest  development.  Here  there  are  developed  numerous  association- 
bundles,  and  the  surface  is  enormously  enlarged,  including  whole  lobes: 
Ldbus  cornu  Ammonis  and  Lobus  pyriformis. 

These  portions  of  the  brain  are  to  be  looked  upon  as  highly-organized 
centers  which  receive  their  stimulation  from  the  lower  olfactory  mechanism, 
but  which,  through  their  structure,'  are  made  capable  of  extended  inde- 
pendent activity. 

Thus,  in  the  vertebrate  series  there  is  added  to  the  lower  olfactory 
mechanism  a  higher  one,  which  gradually  increases  in  extent. 

Having  given  a  general  view  of  the  olfactory  apparatus  as  at  present 
understood  for  the  vertebrates,  let  us  study  in  the  accompanying  figure  (Fig. 


Fig.  100. — Schema  of  the  olfactory  apparatus  of  a  lizard-brain. 


100)  an  ideal  sagittal  section  through  a  lizard-brain,  where  the  parts  already 
described  may  be  again  viewed,  with  their  connections.  The  olfactory  lobe 
lies  anteriorly,  covered  by  the  Formatio  bulbaris,  into  which  the  Fila 
olfactoria  from  the  nasal  mucous  membrane  pass.  Posterior  to  the  Lobus 
olfactorius  lies  the  Area  olfactoria,  and  still  farther  back  the  Nuc.  tasnise 
(Tub.  Than.),  above  which  are  the  epistriatum  and  striatum.  Over 
the  whole  is  spread  the  mantle,  which  bears  the  cortex.  Except  for  the 
mantle  connections,  which  appear  first  in  the  amphibia,  the  schema  holds 
for  all  vertebrates.  That  the  cortical  connections  are  not  absolutely  essential 
to  the  sense  of  smell  is  demonstrated  by  the  fact  that  fishes  have  a  finely 
developed  olfactory  apparatus,  but  possess  no  sort  of  a  cortical  connection. 

All  portions  of 'the  brain  which  are  in  any  way  brought  into  relation 
with  the  olfactory  apparatus  are  connected  with  the  corresponding  portion 


THE  CEREBKUM  OR  PROSENCEPHALON. 


153 


of  the  opposite  side  through  strong  commissural  fibers.  These  bundles  all 
cross  the  median  line  at  one  place,  designated  the  Commissura  anterior. 
This  commissure  lies  in  the  Lamina  terminalis  near  the  base,  and  is  ex- 
ceedingly constant  (Figs.  18,  76,  and  100).  The  various  bundles  are  best 
known  at  present  in  the  reptiles.  Everything  now  known  indicates  that  the 
relations  are  the  same  in  the  other  vertebrates  as  in  reptiles. 

The  commissures  of  the  olfactory  apparatus  are  shown  schematically 
in  Fig.  101. 

II.    THE   CORPUS   STRIATUM. 

The  Corpus  striatum  lies  above  the  olfactory  apparatus.    It  is  a  some- 
what ovoid  body  which  projects  up  into  the  ventricle  of  the  cerebrum  from 


— Tr.septo-ntesoce/jh . 

•-Comniiss.pallfipost 
„  Camm.jjadiii ant. 

\Cbnuuiss.ant. 


Fig.  101. — Schema  of  the  commissures  of  the  olfactory  mechanism  of  the 
reptile  (compare  Fig.  98).  Pars  epistriat.,  Epistriatic  commissure.  Pars  cortical., 
Commissure  of  olfactory  cortex  of  one  hemisphere  with  that  of  other.  Pars 
olfact.,  Ramus  connectens  Lobi  olfactorii. 

the  base  of  the  cerebrum,  occupying  the  same  place  in  all  animals  from  the 
fishes  to  man. 

It  is  not  usually  to  be  seen  in  the  uncut  brain,  because  it  is  covered  in  by 
the  brain-mantle,  and  lies  really  in  the  floor  of  the  enmantled  ventricle. 
Only  in  fishes,  where  the  mantle  is  represented  by  a  thin  membrane,  is  it 
to  be  recognized  through  the  mantle.  In  this  case  it  forms  what  is  called 
the  frontal  lobe.  The  more  highly  developed  the  mantle, — as  in  mam- 
mals,— the  more  unimportant  appears  the  structure — so  large  relatively 


154 


ANATOMY    OF    THE    CENTRAL    NERVOUS    SYSTEM. 


in  the  lower  vertebrates.  In  the  figure  of  the  cod-fish  brain  (Fig.  38)  one 
recognizes  the  corpus  striatum  in  the  large  prominence  at  the  frontal  end. 
If  one  wished  to  change  this  figure  to  represent  a  mammalian  brain,  he 
would  have  to  draw  the  hemispheres,  wholly  wanting  in  the  teleosts,  over 
the  basal  structures  of  the  forebrain.  The  figured  fish-brain  is  to  be  com- 
pared morphologically  to  a  human  brain,  from  which  one  has  dissected  off 
the  hemispheres,  leaving  the  striatum  in  situ. 

The  investigations  of  V.  Gehuchten  on  teleosts  and  those  of  the  author 


Fig.  102. — Frontal  section  of  the  forebrain  of  a  teleost,  bounded  above  by  the 
columnar  epithelium,  which  incloses  the  ventricular  cavity.  The  fish-brain  is 
drawn  within  the  contour  of  a  mammalian  brain  in  order  to  show  the  relation 
in  size  and  position  of  the  structures  under  consideration. 


on  reptiles,  established  the  fact  that,  from  the  great  multipolar  cells  which 
lie  just  in  the  center  of  the  striatum,  large  bundles  of  fibers  arise;  also 
that  fibers  which  come  to  that  organ  from  behind  end  there  in  ramifications. 
The  whole  fiber-system  has  been  previously  designated  the  basal  fore- 
brain-bundle  ;  but  since  all  of  its  fasciculi  end  in  the  ganglia  of  the  thalamus 
or  metathalamus,  a  more  appropriate  name  would  be  Tr.  strio-thalamici. 


THE  CEREBRUM  OR  PROSEXCEPHALOX. 


155 


This  tract  has  already  been  encountered  in  the  description  of  the  interbrain. 
A  careful  review  of  Figs.  72  and  80  will  be  profitable  in  this  connection. 
Through  the  Tr.  strio-thalamici  the  basal  ganglia  of  the  forebrain  are 
most  intimately  connected  with  the  ganglia  of  the  interbrain.  These  tracts 
are  exceedingly  constant,  and,  though  they  are  recognized  with  especial  ease 
in  teleosts  because  of  the  lack  of  other  fiber-systems  from  the  forebrain, 
yet  it  is  possible  to  demonstrate  them  in  amphibians  (Figs.  75  and  80),  in 
reptiles  (Figs.  72,  81,  and  82),  in  birds  (Figs.  83  and  84),  and  in  mammals. 
They  are  naturally  less  prominent  in  the  last,  where  the  fiber-system  from 
the  cortex  to  the  interbrain  and  to  parts  of  the  brain  located  still  farther 
posterior  is  especially  highly  developed.  Their  discovery  was  first  made 


Fig.  103.— Diagrammatic  frontal  section  through  the  brain  of  a  turtle 
(left)   and  of  a  lizard  (right). 


possible  through  embryological  methods;  later,  also,  through  the  study 
of  degenerations.  If  one  remove  the  whole  mantle  from  a  dog's  brain, — a 
feat  successfully  accomplished  by  Monakow  on  the  newborn  animal  and  by 
Goltz  on  the  adult, — all  the  bundles  which  arise  from  the  mantle  degenerate, 
and  those  which  arise  from  the  striatum  remain  intact.  In  the  stained 
section  these  are  brought  out  into  prominence.  In  Fig.  102  it  has  been 
attempted  to  make  the  mantle  more  clear  by  inscribing  a  section  through 
the  corpus  striatum  of  a  teleost  within  the  contour  of  a  human  brain. 
One  sees  at  once  that  the  fiber-system  of  the  striatum  falls  in  the  region 
which  in  mammals  is  designated  as  the  anterior  limb  of  the  Capsula  in- 
terna.  In  the  teleost  the  thin  mantle  is  insignificant  in  comparison  to  the 
striatum;  in  mammals  the  relation  is  nearly  reversed;  but  in  birds,  where 


156 


ANATOMY    OF   THE    CEXTEAL   NERVOUS    SYSTEM. 


the  corpus  striatum  reaches  remarkable  size,  it  makes  the  major  part  of  the 
forebrain,  notwithstanding  the  presence  of  a  fairly  developed  mantle. 

In  turtles  the  enormous  development  of  the  basal  ganglia,  especially 
the  development  of  a  meso striatum,  and  of  the  epistriatum  and  the  disap- 
pearance of  the  lateral  horns  of  the  ventricle  makes  a  cross-section  which  is 
completely  different  from  the  brain  of  other  reptiles,  and  reminds  one 
strongly  of  the  bird-brain  (study  Fig.  103). 

The  chelonian  brain,  with  its  enormous  basal  ganglia  and  slight  de- 
velopment of  the  mantle,  is  more  like  the  avian  brain  than  is  any  other 
reptilian  brain. 

The  Corpus  striatum  of  birds  and  mammals  is,  up  to  the  present,  well 


Fig.  104. — Frontal  section  through  the  brain  of  a  parrot.    A  somewhat  schematic 
composite  of  several  serial  sections  into  one  figure. 


known  only  in  its  principal  features;  much  yet  is  lacking  to  furnish  a  clear 
understanding  of  it,  especially  in  its  subdivisions.  The  author's  experiments 
in  degeneration  show  one  thing,  however:  Neither  in  reptiles,  in  birds, 
nor  in  mammals  can  one  through  removal  of  the  corpus  striatum  cause 
degeneration  of  parts  posterior  to  the  midbrain.  This  indicates  that  that 
important  and  constant  structure,  the  striatum,  confines  its  efferent  fiber- 
system  essentially  to  the  thalamus  and  the  hypothalamus.  The  individual 
bundles  of  the  strio-thalamici  are  developed  to  a  varying  degree,  according  to 
the  size  of  the  thalamic  ganglia  to  which  they  go.  For  example,  the  bundle 
to  the  large  hypothalamus  in  the  teleost  is  enormous, — Tr.  strio-hypothala- 
mus, — while  in  other  animals  it  is  often  difficult  to  find. 


THE  CEREBRUM  OR  PROSENCEPHALON. 


157 


The  higher  vertebrates — the  birds  and  the  mammals — manifest  in  the 
structure  of  the  corpus  striatum  an  especial  construction.  In  mammals  it 
is  divided  into  a  lateral  and  a  median  portion  by  fibers  from  the  cerebral 
cortex  which  bisect  it.  The  lateral  portion  is  designated  as  the  Putamen 
and  the  median  portion  as  the  Nucleus  caudatus.  Several  ganglia — Globus 
pallidus — lie  on  the  median  side  of  the  Putamen,  whose  nature  is  not  yet 
understood,  and  which  are  so  closely  associated  with  the  Putamen  that  they 
are  grouped  with  the  latter,  and  the  whole  ganglion-complex  called  the 
Nuc.  lentiformis.  This  will  be  more  fully  discussed  subsequently.  In  birds 
the  Putamen  and  both  portions  of  the  Globus  pallidus  are  demonstrable,  but 
the  divisions  of  this  portion  of  the  striatum  from  the  Nuc.  caudatus  is  not  so 
sharp  as  in  mammals,  because  the  fibers  from  the  cortex  which,  as  Capsula 
interna  in  mammals,  separates  the  two  portions  are  in  birds  only  slightly 
developed.  Notwithstanding  that,  one  can  with  certainty  recognize  in  birds 


Fig.  105. — Schematic  frontal  sections  of  the  forebrain,  to  show  the  position 
of  the  striatum  and  its  fiber- system  in  relation  to  the  whole.  A,  Brain  of  a 
Teleost;  B,  of  a  Bird;  C,  of  a  Mammal. 


that  from  the  Putamen,  located  extremely  laterally,  a  thick  bundle  passes 
inward,  where  it  meets  those  fibers  which  arise  in  other  parts  of  the  striatum. 
The  two  bundles  together  pass  to  the  nuclei  of  the  thalamus  (see  Figs.  83, 
84,  and  104).  . 

Thus  the  Tr.  strio-thalamici  are  composed  in  the  bird,  as  in  the  mam- 
mal, of  a  median  bundle  and  of  one  which  joins  it  from  the  outer  side. 
The  lateral  bundle  includes  in  mammals  the  greater  part  of  the  fibers  of  the 
cerebral  base  which  pass  down  from  the  cortex.  It  is  there  called  the 
"loop"  of  the  Nucleus  lentiformis.  The  median  portion  corresponds  in  birds 
and  mammals  according  to  its  position  exactly  the  same  as  is  shown  in  Fig. 
102  for  the  fish-brain.  Thus  it  belongs  to  that  collection  of  fibers  which 
is  designated  as  the  Capsula  interna. 


158  ANATOMY    OF    THE    CENTRAL   NERVOUS    SYSTEM. 

Of  the  physiological  significance  of  the  corpus  striatum  we  know 
nothing  at  all.  All  experiments  carried  out  on  the  brains  of  fishes  have  only 
induced  disturbance  of  the  sense  of  smell  when  the  anterior  lobes  were 
severed.  Up  to  the  present  no  animal  from  which  the  striata  alone  had  been 
removed  has  been  observed  for  any  considerable  time.  This  operation  seems 
to  be  possible  only  in  the  teleosts,  where  there  is  no  mantle  to  complicate 
the  operation. 

Even  for  the  olfactory  apparatus,  experiments  which  throw  light  upon 
it  are  few.  It  has  become  possible  only  through  the  experiments  of  the 
last  years  to  give  it  the  anatomical  dignity  of  separating  it  into  different 
territories.  Probably  the  comparative  observation  of  animals  with  a  cortical 
olfactory  apparatus  and  animals  without  it  will  lead  to  the  desired  results. 

The  questions  are:  Do  fishes  smell  in  the  same  manner  as  do  the  higher 
vertebrates?  Do  they  interpret  their  olfactory  impressions  differently? 
Are  they  able  to  retain  these  impressions  in  their  memory? 


CHAPTEE    XII. 

THE  CEREBRUM,  OR  PROSENCEPHALON  (Continued). 

III.    THE   CEREBRAL   MANTLE. 

the  olfactory  apparatus  and  the  corpus  striatum,  we  have  de- 
scribed everything  that  is  common  to  the  Prosencephala  of  all  vertebrates. 
We  come  now  to  the  consideration  of  the  variable  portion  of  the  forebrain, 
namely, .  the  Mantle. 

As  mantle,  or  pallium,  we  have  designated  all  of  those  portions  of  the 
wall  of  the  cerebral  vesicle  not  included  in  the  olfactory  apparatus  and  the 
striatum;  that  is,  the  dorsal  and  lateral  walls  of  the  cerebrum.  It  has 
already  been  mentioned  that  in  several  lower  vertebrates  the  largest  part  of 
it  is  formed  of  a  simple  epithelial  plate.  Of  the  epithelial  mantle  of  the 
teleost  Figs.  86  and  107  furnish  a  sufficient  picture.  In  cyclostomes  portions 
of  the  wall  on  either  side  of  the  basal  ganglion  extend  upward,  ending  in  a 
folded  epithelial  membrane.  Studniczka  has  recently  designated  these 
structures  as  lateral  areas  of  the  mantle.  Their  minute  structure  is,  how- 
ever, too  little  known  to  justify  a  decision.  It  is  possible  that  we  have  to  deal 
here  with  simply  a  dorsally  directed  extension  of  the  striatum.  In  rays  and 
sharks,  representatives  of  the  selachians,  the  mantle  is  developed;  indeed 
the  most  anterior  portion  is  so  enormously  thickened  and  the  lateral  por- 
tions project  so  far  inward  that  in  the  greater  part  of  the  forebrain  of 
selachians  the  ventricle  is  obliterated,  and  in  rays  it  is  to  be  demonstrated  in 
only  the  most  posterior  portions.  In  most  sharks  it  is  present,  and  even  its 
projections  into  the  olfactory  lobes  are  to  be  recognized.  But  even  here, 
since  the  anterior  wall  of  the  brain  is  disproportionately  thickened,  it  pro- 
jects mostly  far  over  the  region  of  origin  of  the  olfactory  lobes,  so  that  they 
do  not  lie  anteriorly,  as  in  the  other  vertebrates,  but  laterally  and  remote 
from  the  frontal  portion  of  the  cerebrum.  In  this  way  the  brain  of  the 
selachian' diverges  much  in  form  from  the  brains  of  other  vertebrates,  as  is 
shown  in  Fig.  106.  It  thus  comes  that  through  the  thickening  of  the  walls 
the  division  into  hemispheres  is  often  so  masked  (Fig.  106,  B)  that  it  is  only 
recognizable  microscopically  through  the  finer  fibers  and  through  the  nar- 
row vascular  cleft  between  the  right  and  left  hemispheres. 

In  the  mantle  of  all  other  vertebrates  a  deep  groove  separates  the  right 
from  the  left  ventricle.  It  reaches  posteriorly  to  the  Lamina  terminalis, 
near  which  the  cerebral  vesicles  have  evaginated.  All  of  the  commissures 

(159) 


160 


ANATOMY   OF   THE    CENTRAL    NERVOUS    SYSTEM. 


which  join  the  hemispheres  to  the  striatum  traverse  the  Lamina  terminalis 
(see  Fig.  101).  In  mammals  for  the  first  time  there  arises  late  in  the  em- 
bryonic period,  dorsal  and  anterior  to  the  Lamina  terminalis,  a  new  system 
of  transverse  fibers  destined  to  connect  cortical  regions  of  one  hemisphere 
with  those  of  the  other:  Corpus  callosum. 

The  mantle  of  higher  vertebrates  is  differentiated  from  those  of  teleosts 
and  ganoids  through  a  very  essential  feature.     It  is  no  longer  simple  epi- 


Fig.  106. — Selachian  brains,  showing  the  various  development  of  the  brain- 
mantle  in  different  species.  A,  Brain  of  Galeus  canis  ;  B,  of  Raja  mlraletus.  C, 
The  cerebrum  of  Carcharias.  All  are  shown  in  natural  size.  In  A  the  Tela 
chorioidea  is  removed,  giving  a  glimpse  of  the  ventricle  of  the  Thalamencephalon. 


thelium,  but  consists  of  numerous  cells  which  receive  and  send  out  nerve- 
fibers;  that  is,  the  mantle  has  become  a  nervous  mechanism.  This  mechan- 
ism, which  is  not  much  developed  in  the  amphibians,  reaches,  in  the  reptiles, 
the  condition  of  a  well  marked  brain-cortex,  differentiated  from  the  other 
layers  of  the  mantle. 


THE  CEREBRUM  OR  PROSENCEPHALOX.  161 

There  is  no  other  part  of  the  brain  which  approximates  the  cerebral 
mantle  in  the  great  changes  in  the  progression  and  retrogression  manifested; 
and,  since  this  is  involved  in  the  existence  of  certain  higher  psychic  activi- 
ties, let  us  now  proceed  with  the  consideration  of  the  most  interesting  field 
of  brain-anatomy. 

First,  as  to  the  outer  form.  What  has  already  been  said  regarding  the 
selachian  mantle  has  shown  that  in  that  class  of  vertebrates  only  the  anterior 
region  of  the  mantle  is  of  nerve-tissue,  but  that  larger  or  smaller  portions — 
according  to  species — of  even  the  posterior  part  of  the  mantle  have  given 
up  the  character  of  simple  epithelium. 

Note  in  Fig.  107  the  thin  mantle  of  the  trout  as  compared  with  the 
enormous  thickening  which  the  anterior  portion  of  the  mantle  has  under- 
gone in  the  ray  (Fig.  108).  Then  note  that  in  the  amphibia  (Fig.  109)  the 
thickening  has  progressed  much  farther  posterior.  Further  note  that  the 


Fig.  107. — Schematic  sagittal  section  of  an  embryonal  teleostean  brain   (trout). 

brain  of  the  reptile,  with  its  already  developing  cortical  substance  (Fig.  110), 
forms  a  transition  to  the  birds,  on  one  side,  and  to  mammals,  on  the  other 
side  (Figs.  Ill  and  112). 

In  our  description  of  the  hemispheres,  which  we  will  always  find  in 
amphibia  and  upward  in  the  vertebrate  series,  it  will  be  best  to  take  as  a 
starting-point  the  ovoidal  form.  In  amphibians  and  reptiles  the  smaller  an- 
terior end  of  the  ovoid  merges  into  the  olfactory  lobes,  while,  on  the  median 
side, — the  one  turned  toward  the  other  hemisphere,— there  takes  place  so 
marked  a  flattening  that  only  a  vertical  cleft  remains  between  the  two  halves 
of  the  brain. 

In  the  midst  of  the  cleft  the  two  halves  of  the  brain  are  connected  by 
the  unpaired  Lamina  terminalis,  which  passes  in  a  convex  line  from  above 
downward  and  forward.  But  the  hemispheres  have  been  developed,  not  only 
anteriorly  from  the  Lamina  terminalis,  as  is  stated  in  the  embryological  in- 
troduction. They  usually  extend  dorsally  as  well  as  ventrally  from  the 


162 


ANATOMY  OF  THE  CENTRAL  NERVOUS-  SYSTEM. 


lamina.     The  dorsal  portion  is  directed  posteriorly  and  may  be  designated 
as  the  Polus  occipitalis  pallii. 

The  ventral  projection,  which  is  present  only  in  a  rudimentary  form  in 
amphibians  and  reptiles  (Fig.  113),  should  be  called  Polus  temporalis.  Into 
both  these  poles  the  ventricular  cavity  extends,  forming  a  posterior  liorn 
and  an  inferior  horn. 


Fig.  108.— Sagittal  section  of  a  selachian  brain   (the  ray). 

The  nearly  ovoid  hemispheres  of  the  amphibian  correspond  most  closely 
to  this  schematically  described  brain.  But  even  in  the  reptiles  the  outer 
form  manifests  quite  marked  variations  in  the  development,  according  to 
the  families.  When  one  finally  passes  up  through  the  birds  and  mammals 
he  soon  meets  the  widest  variations  in  form. 


Fig.   109. — Sagittal  section  of  an  amphibian  brain. 


At  first  there  is,  in  amphibians,  a  hardly  noticeable  groove  between  the 
olfactory  lobe  and  the  mantle,  running  outward  and  downward  on  the  mar- 
gin of  the  mantle,  called  the  Fovea  linibica.  This  groove,  separating  the 
olfactory  apparatus  from  the  mantle,  is  always  clearly  marked  in  mammals. 
The  development  of  the  individual  poles  offers  essential  differences.  Some 
have  suggested  for  the  Polus  frontalis  of  the  lower  vertebrates  the  term 


THE    CEREBRUM    OR   PROSENCEPHALON. 


163 


frontal  lobe,  for  the  Polus  occipitalis,  temporal  lobe,  etc.  But  this  is  in- 
correct, since  that  which  bears  the  name  in  mammals  is  a  product  of  late 
development.  For  example,  the  occipital  lobe  of  mammals  does  not  exist  at 
all  in  reptiles.  It  appears  for  the  first  time  in  birds.  The  occipital  lobe  is 


Fig.  110. — Schematic  sagittal  section  of  a  reptilian  brain. 

not  alone  a  prominence  of  the  occipital  pole,  but  a  definite  portion  of  cere- 
brum with  a  specialized  cortical  character  and  a  fixed  relation  to  the  origin 
of  the  Opticus. 

So  we  find  that  even  in  the  lower  vertebrates  the  form  of  the  brain 


Fig.  111. — Schematic  sagittal  section  of  an  avian  brain. 

varies  in  different  orders.  When,  for  example,  one  compares  the  above 
illustrated  lizard-brain  with  that  of  a  turtle  the  compressed  form  of  the 
latter  will  certainly  be  apparent.  It  is  brought  about,  on  the  one  hand,  by 
the  development  of  the  striatum,  which,  as  above  described,  causes  a  simi- 


164 


ANATOMY    OF    THE    CENTRAL   XEBVOUS    SYSTEM. 


larity  between  the  turtle-brain  and  the  avian  brain;  and,  on  the  other  hand, 
by  the  development  of  the  skull,  which  is  never  without  influence. 

In  higher  vertebrates  with  the  great  development  of  the  mantle  appear 
the  grooves,  or  sulci.     Since  they  are  particularly  developed  in  the  mam- 


Fig.  112. — Schematic  sagittal  section  of  a  mammalian  brain. 

malian  brain,  they  will  be  minutely  described  in  a  later  chapter.  The  brains 
of  most  reptiles  possess  only  the  Fovea  limbica  as  boundary  between  two 
different  portions  of  the  mantle.  However,  there  is  recognizable  in  the  large 
snakes  and  still  better  in  turtles  another  shallow  groove,  which  lies  near  the 


Fig.  113. — External  view  of  the  brain  of  the  lizard:     Varanus. 
(Enlarged  four  times.) 

upper  edge  of  the  mantle  and  extends  for  a  shorter  or  longer  distance  parallel 
to  it.  In  birds  this  Fovea  collateralis  is  more  clearly  developed.  It  is  not  a 
real  sulcus  such  as  traverse  the  mammalian  brain.  We  have  to  do  here  with 
a  ventral  and  dorsal  projection  of  the  mantle,  which  is  dependent  upon  the 


THE    CEREBRUM    OR    PliOSKXC  K  i'HALON". 


165 


development  of  the  striatum  (see  Fig.  105,  B).  Between  the  two  projections 
remains  the  groove,  which  has  been  designated  the  Fovea  collateralis. 

Somewhat  more  complicated  than  the  arrangement  of  the  outer  aspect 
of  the  hemispheres  is  that  of  the  median  wall.  In  the  amphibia  this  wall  has 
undergone  so  little  differentiation,  that  in  certain  species — indeed,  in  differ- 
ent specimens  of  the  same  species — it  may  be  grown  to  the  adjacent  wall  of 
the  other  hemisphere  for  a  greater  or  less  distance. 

Such  is  not  the  case  in  reptiles.  While  all  the  features  to  be  here  de- 
scribed are  present  in  amphibia  in  a  rudimentary  form,  it  is  only  in  the 
highly  organized  reptilian  brain  that  they  come  out  into  prominence.  Here 
one  can  easily  make  several  subdivisions,  subdivisions  which,  as  will  be 
brought  out  later  in  the  description  of  the  mammalian  brain,  will  serve  as 
important  points  of  departure  in  following  its  further  development. 


Fig.  114. — Inner  wall  of  a  hemisphere  of  the  reptilian  brain: 
from  Taranus  griseus. 


1.  The  median  surface  of  the  olfactory  apparatus  near  the  base:  Area 
parolfactoria.    In  reptiles  there  are  prominent  aggregations  of  ganglia  here, 
which  give  rise  to  bundles  of  fibers. 

2.  Posterior  to  this  and  somewhat  farther  dorsal  lies  that  portion  of  the 
median  wall  designated  the  Septum,  which  also  contains  a  ganglion  in  rep- 
tiles, in  birds  is  strongly  atrophied,  while  in  mammals,  again,  it  contains  a 
small  ganglion  and  is  called  the  Septum  pellucidum,. 

3.  Dorsal  to  the  two  portions  named  is  the  cortical  portion  of  the  inner 
wall. 

In  the  dorsal  portion  of  the  area  parolfactoria  there  begins  regularly 
a  deep  sulcus,  which,  running  to  the  Lamina  terminalis  in  the  upper  margin 


166 


ANATOMY    OF   THE    CENTRAL    NERVOUS    SYSTEM. 


of  the  septum,  divides  the  whole  inner  side  into  a  dorsal  and  a  ventral  por- 
tion. Only  the  dorsal  portion  is  covered  with  cortical  tissue.  This  sulcus, 
which  thus  forms  the  ventral  boundary  of  the  brain-cortex,  persists  through- 
out the  whole  animal  series  after  its  appearance  in  the  reptiles.  In  the 
accompanying  figure  (114)  it  is  called  Fissura  arcuata  septi,  but  in  mammals 
it  is  called  the  "inner  marginal  fissure/' 

Into  the  cortex  which  covers  the  dorsal  portion  of  the  septum  an  im- 
portant bundle  regularly  enters:  the  Tr.  olfactorius  septi.  It  arises  from 
the  olfactory  apparatus  of  the  base  of  the  brain;  its  fibers  converge  toward 
the  median  brain-surface,  thence  pass  upward  and  backward  into  the  cortex. 
The  region  in  which  it  ends  is,  on  this  account,  called  the  olfactory  cortex. 
In  amphibia,  with  uncertainty,  demonstrable;  this  bundle  is  always  promi- 


Fig.  115. — Sagittal  section  through  the  brain  of  a  chicken. 


nent  in  reptilia  and  mammalia  (see  Fig.  114).  In  birds,  however,  it  is  veiled 
by  a  bundle,  which  is  especially  developed  in  these  animals — Tr.  septo- 
mesencephalicus — and  which,  arising  in  a  wide  origin  from  the  dorsal  portion 
of  the  cortex  near  its  edge  where  it  turns  outward,  is  spread  out  upon  the 
inner  surface  of  the  avian  brain  like  a  broad,  white  fan.  Reaching  the  base 
of  the  brain,  it  encircles  it  with  externally  directed  fibers,  and  just  anterior 
to  the  optic  tract,  which  it  reaches  on  the  lateral  aspect  of  the  brain,  passes 
again  upward  and  backward  to  disappear  in  the  most  anterior  portion  of  the 
roof  of  the  midbrain.  Thus  this  tract  connects  the  midbrain  with  a  par- 
ticular cortical  region  (Fig.  115).  It  is  foreshadowed  in  reptiles,  but  has 
not  been  located  in  mammals. 

If  one  makes  a  frontal  section  through  the  forebrain  of  any  of  the 


THE    CEREBKOI    OR    PROSEXCEPHALOX. 


167 


higher  vertebrates,  the  more  anterior  sections  always  show  an  approximately 
oval  outline  on  whose  base  the  corpus  striatum  lies  (see  Fig.  103);  farther 
posterior  (Fig.  101)  one  finds  the  septum  on  the  inner  wall,  which  loses  its 
previously  simple  features;  and  finally  one  comes  (Fig.  99)  to.  the  place 
where  the  mantle  merges  into  the  choroid  plexus  and  becomes  purely  epithe- 
lial (Fig.  120).  At  this  point  in  the  base  of  the  brain  the  boundary  between 
the  forebrain  and  the  interbrain  is  usually  reached,  and  one  sees  upon  the 
sections  the  tracts  which  unite  these  two  segments  of  the  brain. 

The  author  assumes  that  this  brief  description  illustrated  by  the  figures 
has  sufficiently  familiarized  the  reader  with  the  outer  form  of  the  cerebrum, 
and  will  now  describe  the  structure  of  certain  parts  of  the  mantle. 

As  the  cross-sections  of  the  whole  amphibian  brain  is  strikingly  like 
the  embryonic  brains  of  the  other  vertebrates,  so  even  in  the  forebrain  a 
structure  will  be  found  which  always  recurs  in  higher  vertebrates  in  the 


Fig.  116. — Section  through  the  mantle  of  a  frog-brain.     (After 
Pedro  Ramon  y  Cajal.) 


embryonic  period.  Thus,  one  can,  in  a  section  through  "the  cerebral  wall, 
usually  differentiate  only  two  layers:  an  inner  one  rich  in  cells  and  an  outer 
one  sparsely  filled  with  cells.  At  several  places  in  the  mantle, — near  the 
olfactory  apparatus,  for  example, — in  the  anterior  part  of  the  Eegio  parolfac- 
toria,  and  then  in  the  postero-median  region  of  the  mantle  the  inner  layer 
shows  especial  projections:  evidently  a  greater  development  of  the  cells 
which  constitute  it.  Good  sections  well  stained  show  that  the  inner  layer 
next  to  the  ventricle  is  formed  of  epithelial  cells,  which  send  their  long 
branching  processes  up  through  the  entire  mantle  to  the  outer  surface,  thus 
making  a  frame- work  for  the  brain-mantle  (see  Fig.  116,  the  left  margin). 
This  frame-work,  formed  of  the  terminal  processes  of  epithelial  cells,  is,  be- 
sides this,  present,  also,  in  all  portions  of  the  brain  posterior  to  this,  and  is 
persistent  even  in  the  reptilia.  In  birds  and  mammals  a  large  part  of  the 
terminal  processes  disappear  in  post-embryonal  life.  Then,  farther  outward 


168  ANATOMY    OF    THE    CENTRAL    NEEVOUS    SYSTEM. 

there  are  numerous  cells,  which,  for  the  most  part,  cannot  be  recognized  as 
ganglion-cells,  but  rather  retain  the  character  of  neuroblasts  throughout  life. 
Between  them,  however,  lie  true  ganglion-cells,  with  profusely  branching 
dendrites  and  slim  neuraxons.  The  majority  of  these  neuraxons  may  be 
traced  upward  toward  the  brain-surface;  but  a  small  minority  take  their 
course  between  the  ganglion-cells  and  the  epithelial  cells,  and  mark  the  be- 
ginning of  the  subcortical  medullary  layer.  Whither  they  go  in  amphibia  is 
not  known,  but  it  is  probable  they  go  mostly  in  the  commissures  of  the 
mantles.  From  single  fibers  which  pass  outward  from  this  subcortical 
medullary  layer  and  from  those  which  pass  direct  from  the  cells  to  the  sur- 
face of  the  brain  there  is  formed  just  under  the  surface  of  the  brain  a  fine 
net-work:  the  tangential  reticulum.  Besides  the  two  sources  named,  the 
neuraxons  of  cells  which  lie  in  the  tangential  reticulum  itself  participate  in 
the  formation  of  the  net-work. 

This  quite  irregularly  disposed  apparatus  must  be  looked  upon  as  the 
fundament  of  a  brain-cortex,  because  in  reptiles  one  finds  just  the  same 
elements,  only  in  much  greater  number  and  thickness,  arranged,  further- 
more, in  more  regular  and  unmistakable  strata.  In  these  animals  no  fur- 
ther doubt  can  exist  that  one  has  in  this  structure  to  deal  with  a  cortex, 
from  which,  as  we  shall  see  later,  the  highly  specialized  and  well  known 
cortex  of  higher  vertebrates  may  be  derived. 

It  is,  indeed,  one  of  the  greatest  services  which  S.  Ramon  y  Cajal  has 
bestowed  in  the  field  of  brain-anatomy  that  he  has  demonstrated  the  type 
which  recurs  in  the  structure  of  the  brain-cortex  in  all  classes  of  vertebrates 
and  that  he  designated  the  features  that  characterize  a  brain-cortex.  The 
author's  own  investigations  on  amphibia  and  reptilia  coincide  throughout 
with  the  important  discovery  of  the  Spanish  savant. 

A  most  essential  feature  of  the  cortical  structure,  and  one  always  recog- 
nizable, is  the  fact  that  these  fibers  originate  and  end,  and  that  there  exist 
innumerable  possibilities  for  the  association  of  incoming  and  outgoing  fibers. 

In  the  cortex  of  the  reptile  one  may  from  without  inward  differentiate 
(1)  the  tangential  layer  of  fibers,  (2)  a  molecular  cell-layer,  (3)  a  layer  of 
pyramidal  cells,  (4)  the  layer  of  the  Plexus  subcorticalis,  (5)  the  medullary 
center,  and  (6)  the  ventricular  epithelium  (compare  Fig.  117). 

This  relatively  simple  apparatus  is,  however,  so  constructed,  even  in 
vertebrates  of  so  low  rank  as  the  reptiles,  that  it  affords  an  almost  infinite 
possibility  for  combinations  of  single  cells  and  tracts  (study,  again,  Fig.  117). 

But  the  cortex  is  not,  by  any  means,  uniform  over  the  whole  mantle. 
Even  in  reptiles  one  can  differentiate  particular  cortical  areas  one  from 
another.  The  author  would  differentiate  at  least  three  separate  areas  in 
the  cortex  of  the  reptile  (see  Fig.  103),  to  which  might  be  added  as  a  fourth 
the  cortex  on  the  Conus  frontalis  pallii,  which  belongs  possibly  to  the  olfac- 


THE    CEREBRUM    OR    PROSEXCEPHALOX. 


169 


tory  apparatus;  furthermore,  this  area  sends  out  a  separate  bundle  which 
probably  ends  in  the  thalamus.  Of  those  cortical  portions  depicted  in  Fig. 
103,  the  one  designated  as  dorso-median  area  is  especially  interesting.  It 
covers  the  whole  median  side  of  the  brain,  passes  the  dorso-median  edge, 
extends  out  laterally  over  the  outer  surface  of  the  brain,  and  includes  that 
olfactory  bundle  mentioned  in  the  last  chapter.  External  to  this  and  sepa- 
rated from  it  by  a  narrow  cleft  lies  another  interesting  cortical  portion. 
This,  the  dorsal  area  or  plate,  covers  not  only  the  dorsal  portion  of  the 


Fig.  117.  —  Section  of  cortex  near  median  dorsal  edge  of  the  mantle  of 
Lacerta  agilis.    Golgi  staining. 


outer  wall,  but  turns  toward  the  median  line  on  the  ventral  surface  covering 
the  epistriatum.  These  relations  are  preserved  throughout  life  in  the  turtle. 
They  are  well  shown  in  Fig.  118.  Note,  also,  in  this  figure  how  the  medul- 
lated  tangential  layer  bends  inward  toward  the  epistriatum.  Note,  also,  the 
Tr.  bulbo-epistriaticus.  Ventral  from  the  dorsal  plate  lies  the  lateral  plate, 
which  adheres  closely  to  the  striatum  (is  possibly  identical  with  it),  called, 
in  mammals,  the  Claustrum. 

It  is  interesting  to  note  that  the  cortical  area  which  receives  the  oft- 
mentioned  olfactory  bundle  remains  on  the  inner  edge  of  the  hemisphere, 
not  only  in  the  reptiles,  but  also  in  mammals.  In  most  reptiles  it  presents 


170 


ANATOMY    OF    THE    CENTRAL   NERVOUS    SYSTEM. 


a  smooth  surface,  but  in  several  species  one  recognizes  that  it  experiences  an 
increase  in  area  through  folding.  In  mammals  this  folding  reaches  the  ex- 
tent of  a  complete  rolling  in  of  the  whole  cortex,  at  least  in  adults,  while  in 
the  embryonic  state  the  relations  are  the  same  as  in  reptiles,  where  the  struct- 
ure first  made  its  appearance  (see  Fig.  119). 

This  rolled  in  portion  of  the  cortex  that  always  receives  a  bundle  from 


Fig.  118. — Frontal  section  through  a  hemisphere  of  the  giant  turtle:    Chelone  midas. 

the  olfactory  apparatus  has  long  since  been  designated  as  the  Cornu 
Ammonis. 

The  investigation  of  the  amphibian  brain  makes  it  very  probable  that 
exactly  the  corresponding  region  of  the  mantle-wall  receives  olfactory  con- 
nections. 

Broca,  and  later  Zuckerkandl,  demonstrated,  after  numerous  compari- 
sons, that  in  mammals  the  extension  of  Ammon's  horn  and  the  cortex  lying 
anterior  to  it  under  the  limbic  fissure  is  completely  dependent  upon  the 


THE  CEREBRUM  OR  PROSEXCEPHALOX. 


171 


•development  of  the  olfactory  apparatus;  so  dependent  that,  in  aquatic  mam- 
mals with  atrophied  olfactories,  this  cortical  area  is  demonstrable  only  in 
rudimentary  form,  while  in  the  burrowing  rodents  it  may  attain  an  enor- 
mous development. 

Through  these  investigations  the  demonstration  seems  complete  that 
the  cortical  portion  just  described  is  the  cortical  center  for  the  sense  of 
;smell. 

Xot  only  does  a  fiber-system  end  in  the  Cornu  Ammonis,  but  a  bundle 
arises  from  it  and  commissures  enter  it.  A  large  assortment  of  fibers  come 
into  relation  with  this  cortical  area.  Before  they  enter  they  all  distribute 
themselves  along  the  ventral  margin  and  form  an  important  collection  of 
nerve-fibers  designated  the  Fimbria.  The  fimbria  always  occupies  the  same 


Fig.  119. — Section  through  the  posterior  portion  of  the  left  hemisphere:    A,  of  a 
Lizard — Yaranus  griseus;    B,  of  a  Mouse-embryo. 


position  in  all  vertebrates;  it  accompanies  the  ventral  margin  of  the  cornu, 
and,  therefore,  in  reptiles  lies  dorsal  to  the  Fissura  arcuata  septi.  In  the 
posterior  portion  of  the  hemispheres  where  the  median  wall  of  the  brain 
merges  into  the  Plexus  chorioideus  the  fiber-system  of  the  fimbria  lies  be- 
tween these  structures  and  the  cortex.  Let  us  now  consider  the  fibers  which 
arise  in  the  olfactory  cortex,  and  also  the  commissural  fibers. 

Reptiles  and  mammals  which  have  well-developed  olfactory  cortices, 
probably  also  amphibians  and  birds,  possess  two  bundles  which  characterize 
this  cortical  region  and  always  occur  in  the  same  place.  The  two  bundles 
are  generally  together  designated  the  Fornix.  But  it  is  more  advisable  to 
subdivide  the  bundle  into  two  parts  according  to  their  terminations.  Com- 
ing from  the  posterior  part  of  the  olfactory  cortex  they  together  pass  a 
short  distance  ventrally  to  about  the  level  of  the  commissura  anterior,  and 
then  they  turn  toward  the  posterior.  Here  the  previously  united  bundle 


17! 


AXATOMY    OF    THE    CENTRAL    NERVOUS    SYSTEM. 


divides  into  two  parts:  one  bundle  going  to  the  Ggl.  habenulse, — Tr. 
Cortico-habenularis, — and  another  one  to  the  Corpus  mamiUare  on  the  base 
of  the  hypothalamus, — Tr.  cortico-mamillaris  (see  Fig.  100).  The  latter, 
especially,  is  a  well  denned  bundle  easily  followed  in  its  course,  long  known 
in  mammals  as  the  Fornix  column.  In  birds  it  is  very  thin.  In  birds  and 
reptiles  the  fornix  passes  in  a  rather  straight  course  from  its  origin  to  its 
terminus.  But  in  mammals,  where,  through  the  great  development  of  the 
mantle,  the  olfactory  cortex  recedes  far  to  the  posterior  and  in  part  bends 
ventrally  (Figs.  132,  133,  and  143),  the  Tr.  cortico-mamillaris  must  follow 


Medio-dors.  cortex.  Ammou's  horn 


Epistriatum 

Post,  end  of  septum  fiinbria 

Fiss.  arcuat.  septi 

Plexus  chorioid. 

Tjenia 

Tr.  thalamo-mamill. 

Tr.  olf.  habenul. 

Fornix 

Tr.  strio-thalamicus 
Tr.  septo-mesencephalicus 


Fig.  120. — Frontal  section  through  the  posterior  cerebral  portion  of  the 
giant  snake:  Python  bivittatus.  Dorsal,  the  mantle;  ventral,  the  transitional 
region  of  the  Thalamus. 


the  margin  of  the  hemisphere  and  run  a  rather  long  arcuate  course  before 
it  can  turn  down  to  the  corpus  mamillare  just  behind  the  commissura 
anterior. 

Besides  the  Fornix  system  the  olfactory  cortex  is  characterized  by  a 
commissural  system  which  connects  the  right  side  with  the  left.  Its* 
bundles  are  designated  as  Commissura  ant.  and  post,  pallii.  In  mammals 
the  whole  complex  is  called  the  Psalterium.  In  the  lowest  orders  of  mam- 
mals it  forms  the  only  mantle  commissure;  in  the  higher  orders  there  is  a 
second  commissure,  the  Corpus  callosum.  The  latter  connects  mantle-areas 
which  do  not  belong  to  the  olfactory  apparatus,  and  is  usually,  especially  in 
man,  much  larger  than  the  commissures  of  the  olfactory  mantle,  because, 


THE    CEREBRUM    OR    PROSEXCEPHALOX.  173 

as  we  shall  see  later,  of  the  high  development  of  mantle  not  yet  described. 
The  corpus  callosum  always  lies  dorsal  to  the  olfactory  commissure  and  is 
naturally  correspondingly  longer  and  thicker  the  more  the  mantle  is  ex- 
tended. It  is  longest  in  apes  and  in  man  and  shortest  in  rodents  and  in 
insectivora. 

The  physiological  significance  of  the  brain-cortex  has  come  to  be  known 
through  a  great  number  of  admirable  studies  on  the  mammalian  brain  in  the 
course  of  the  last  twenty-five  years.  The  experiments  upon  animals  and 
the  observations  upon  man,  observations  which  daily  lead  to  new  and  inter- 
esting results,  have  yielded  the  following:  The  cortex  may  be  accepted  as  that 
part  of  the  brain  tvhich  serves  as  the  basis  of  the  highest  psychic  functions. 
Upon  the  normal  existence  and  condition  of  the  brain-cortex  depend  all  of  those 
abilities  which  may  be  acquired  by  study,  nearly  all  of  those  activities  which  are 
executed  by  the  use  of  memory-pictures,  and  especially  all  of  those  psychic 
processes  which  we  term  associations. 

One  may  conceive  the  whole  cortical  apparatus  as  a  gigantic  association- 
center,  to  which  from  without  through  relatively  narrow  tracts  such  impres- 
sions may  be  conducted  as  have  already  found  their  first  termini  in  deeper 
centers:  primary  brain-centers.  From  this  cortical  association-center  tracts 
pass  down  to  more  posterior  brain-regions  which  are  adapted  to  call  forth 
movements,  etc.,  through  their  agency.  The  sum  of  all  these  tracts  is  desig- 
nated Corona  radiata. 

That  which  determines  the  size  and  extent  of  the  cortex-bearing  mantle 
is  not  the  usually  narrow  tracts,  but  the  development  of  the  association- 
fibers  which  afford  the  possibility  to  receive  the  afferent  sensory  impressions 
in  the  very  greatest  variety  of  ways,  to  inhibit  or  suppress,  to  evaluate,  to 
associate  with  previously  received  ones,  and  finally  to  harmonize  the  activi- 
ties with  acquired  memory-pictures.  We  know  also  that  special  activities  are 
performed  by  special  cortical  areas;  that  the  cortex  subdivides  into  a  num- 
ber of  separate  regions  which  are  functionally  different.  Numerous  investi- 
gations of  the  last  years  have  made  us  more  definitely  acquainted  with  the 
surface  of  the  mammalian  brain-mantle.  The  results  of  these  investigations 
taught  us  that  certain  areas,  varying  according  to  the  species,  are  more 
developed,  and  certain  ones  less  so.  Our  knowledge  of  the  physiological 
significance  of  these  cortical  areas  is,  in  many  cases,  slight,  but  it  is  the  task 
of  the  immediate  future  to  study  the  development  of  these  cortical  areas: 
a  task  which,  happily,  is  already  undertaken  for  certain  species  of  mammals. 

Thus,  since,  according  to  the  present  state  of  our  knowledge,  the  cortex 
may  be  accepted  as  the  location  of  those  psychic  functions  which  are  con- 
sciously executed  after  consideration,  through  use  of  memory-pictures,  so 
is  the  demonstration  of  a  cortical  bundle  to  the  nucleus  of  a  special  sensory 
apparatus  of  great  interest  to  comparative  psychology. 


174  ANATOMY    OF    THE    CEXTEAL   XERVOUS    SYSTEM. 

Hence  it  seems  to  me  the  most  important  result  under  consideration 
up  to  the  present  time,  that  we  have  been  able  to  demonstrate  that  the  first 
cortical  area  developed  in  the  animal  kingdom  was  the  olfactory  cortex.  The 
olfactory  cortex  is  the  cortex  of  the  dorso-median  area,  because  just  this  area 
is  where  the  fibers  from  the  terminus  of  the  secondary  olfactory  tract  end. 
A  clew  which  could  throw  light  on  the  functional  significance  of  other  cor- 
tical areas  in  reptiles  has  not  been  found.  They  may  belong  to  the  olfactory 
apparatus,  but  not  necessarily  so. 

That  the  oldest  cortex  represents  essentially  only  a  single  sensory  center 
— the  olfactory  center;  that  all  associations  which  serve  them  as  a  founda- 
tion, all  memory-pictures  which  they  retain,  are  such  as  serve  especially  the 
sense  of  smell;  these  facts  furnish  a  point  of  departure  for  new  investiga- 
tions in  the  field  of  comparative  psychology.  Studies  in  animal  psychology 
have,  up  to  the  present  time,  been  based  upon  too  complicated  psychic 
phenomena.  We  must  first  know  what  sensory  impressions  a  lower  animal 
may  receive,  what  it  may  retain,  and  how  far — directly  or  through  associative 
thought — it  is  able  to  interpret  these  impressions.  Then  only  shall  we  be 
prepared  to  approach  the  complicated  problems  which  have  usually  been 
attempted. 

Let  us  now  turn  back  to  the  purely  morphological  considerations,  and 
determine  first  how,  in  the  course  of  the  vertebrate  series,  other  tracts  have 
been  associated  with  the  cortical  olfactory  tracts;  how  the  complicated 
apparatus  which  we  see  in  the  mammalian  brain  came  to  be. 

Unfortunately  there  is  not  much  that  can  be  reported.  There  are 
everywhere  gaps  in  our  knowledge,  everywhere  it  requires  more  diligent 
collaboration  in  the  field  only  recently  discovered. 

We  have  set  aside  the  olfactory  center  while  we  studied  the  connections 
which  joined  the  olfactory  apparatus  with  the  cortex.  Though  we  may  not 
find  with  certainty  also  in  reptiles  another  and  similar  connection,  we  may 
turn  to  the  avian  brain,  which  will  furnish  a  number  of  other  bundles  con- 
necting the  cortex  with  parts  of  the  brain  lying  farther  back. 

Most  interesting  to  me  from  the  stand-point  of  comparative  psychology 
is  the  bundle  which  arises  in  the  occipital  region  of  the  brain,  passes  forward 
to  bend  sharply  downward  and  backward,  arid  thence  passes  to  the  termini 
of  the  optic  nerve  in  the  midbrain.  The  Tr.  Occipito-mesencephalicus  is  so 
enormously  developed  in  the  pigeon  that  it  appears  to  be  one  of  the  very 
largest  bundles  of  the  whole  brain.  The  reptiles  possess,  apparently  in  the 
same  location,  a  thin  bundle;  it  is  not,  however,  absolutely  certain.  A 
pigeon  in  which  one  has  severed  this  bundle  appears  to  be  blind  in  the  eye 
on  the  side  opposite  the  severed  bundle,  taking  its  bearings  with  difficulty 
and  always  with  the  eye  that  has  the  uninjured  central  visual  field.  We 
know  that  up  to  mammals  and  man  there  exists  such  a  tract  from  the 


THE  CEEEBRUM  OR  PROSEXCEPHALOX. 


175 


primary  optical  centers  to  the  occipital  lobes,  and  I  will  show  later  how  in 
mammals  all  of  those  functions  which  we  conceive  as  "seeing  with  under- 
standing, recognition  and  interpretation"  are  dependent  upon  the  entirety 
of  the  occipital  lobe.  Thus,  in  birds,  first  in  the  series,  the  primary  optical 
apparatus  is  connected  with  the  cortical  mechanism.  Undoubtedly  a  greater 
capacity  for  service  is  thus  made  possible  for  the  visual  apparatus. 

It  will  now  be  more  easily  understood  how  birds  work — in  part — with 
very  highly  developed  possibilities  for  visual  memories.  The  interpretation 
of  olfactory  impressions  may  be  sufficient  for  the  supply  of  life-necessities  for 
the  earth-groveling  lower  vertebrates,  but  for  birds  the  same  thing  would 
not  be  advantageous.  For,  flying  far  above  their  food,  their  homes,  etc.,  they 


Fig.    121. — Composite  of  several   lateral  sagittal  sections  from   a  pigeon's  brain 
showing  the  course  of  the  Tr.  occipito-mesencephalicus. 


must  be  able  to  recognize  these  by  sight,  and,  more  than  that,  to  differentiate 
them  from  all  other  similarly  appearing  objects.  Eecall  in  this  connection 
the  unerring  swoop  of  the  bird  of  prey  upon  its  victim;  the  migrations,  the 
certain  return  of  the  carrier-pigeon,  etc. 

Another  bundle  which  arises  in  the  cortex  of  the  avian  brain  has  been 
mentioned  already — the  Tr.  Septo-mesencephalicus  (Fig.  115).  This  stands 
in  close  connection  with  the  terminations  of  the  optic  nerve  and  with  the 
sensory  functions  of  the  midbrain.  Regarding  the  functions  whose  bearer  it 
is  we  know  nothing  as  yet  with  much  certainty.  Its  severing  does  not  cause 
disturbance  of  vision  (Jensen),  nor  does  it  cause  indubitable  motor  dis- 
turbances. 


176  ANATOMY    OF   THE    CENTRAL   NERVOUS    SYSTEM. 

We  are  yet  far  short  of  answering  the  question  which  presents  itself  at 
once  after  these  observations:  What  functions  has  the  primary  end-appa- 
ratus— i.e.,  the  deep  center — of  the  sensory  nerves  in  the  brain?  We  know 
simply  what  occurs  in  mammals  when  they  are  deprived  of  their  connection 
with  cortical  center.  Now,  it  is  not  at  all  improbable  that,  in  the  measure 
that  the  psychical  activity  of  the  cortex  increases,  the  activity  of  the  deeper 
center  decreases.  Fortunately  we  possess  in  the  teleosts  organisms  which 
possess  no  cortex  at  all  and  only  the  lower  centers.  On  these  new  observa- 
tions should  be  instituted.  It  is  asked:  What  is  the  reptile  more  capable  of 
accomplishing  in  the  realm  of  smell — in  the  interpretation  of  his  olfactory 
perceptions — than  a  fish,  now  that  it  is  demonstrated  that  to  the  olfactory 
apparatus  of  the  reptile  a  cortical  center  has  been  added?  Similar  investiga- 
tions are  needed  for  the  visual  apparatus,  since  a  difference  must  exist  be- 
tween the  vision  of  a  teleost,  whose  optic  tract  ends  in  the  midbrain,  and 
that  of  a  bird  or  mammal,  which  possesses,  from  the  primary  optical  center 
to  the  cerebral  cortex,  a  tract  which  meets  there  an  extension  association- 
apparatus. 

The  brain-cortex  enters  into  connection  with  a  number  of  connections 
which  are  located  far  posterior  to  the  cerebrum.  These  come  into  promi- 
nence for  the  first  time  in  all  their  complexity  in  the  mammals,  and  we  shall 
have  to  study  them  more  closely  when  the  mammalian  brain  is  under  con- 
sideration. But  as  low  in  the  series  as  the  reptiles  one  finds  a  portion  of 
the  Corona  radiata  coming  from  the  frontal  pole  and  ending  probably  in  the 
Thalamus — Tr.  cortico-thalamicus.  This  very  cortico-thalamic  connection 
becomes  later  very  strong,  as  already  incidentally  mentioned  in  the  descrip- 
tion of  the  thalamic  nuclei.  Other  very  thin  fasciculi  of  the  Corona  radiata 
have  been  observed  in  birds,  but,  since  their  termini  are  insufficiently  known, 
their  enumeration  would  be  of  little  interest  here.  Though  there  are  in 
reptiles  and  birds  no  cortical  connections  to  parts  which  lie  posterior  to  the 
thalamus,  yet  such  connections  occur  in  mammals  more  and  more  in  the 
ascending  animal  series.  The  cortex  becomes  ever  larger,  ever  more  im- 
portant for  the  activity  of  the  animal  organism  when  the  mechanisms  which 
develop  under  the  influence  of  use  and  thought  are  perfected. 

The  great  importance  of  the  brain-cortex  for  activity  in  association  is 
evident,  not  only  from  the  observations  which  have  been  made  on  animals 
deprived  of  cortical  areas  and  on  men  with  diseased  cortical  areas,  but  also 
from  its  structure,  since,  as  you  have  already  seen,  the  cortex  of  the  reptiles 
affords  extraordinarily  great  possibilities  for  association  of  afferent  impres- 
sions. Innumerable  contacts  connect  there  the  cells  and  the  tracts  of  the 
most  varying  provinces.  In  birds,  but  still  more  in  mammals,  there  are  still 
several  long  bundles  which  pass  from  one  portion  of  the  cortex  to  another. 
These  are  called  Association-bundles.  In  Fig.  121  there  may  be  seen  de- 


THE  CEREBEUM  OE  PEOSEXCEPHALON. 


177 


picted  in  the  pigeon  two  of  these  bundles  which  are  for  the  purpose  of  con- 
necting the  frontal  with  the  occipital  segment  of  the  mantle.  The  dorsal 
one  passes  close  beneath  the  cortex,  while  the  ventral  one  passes  over  the 
surface  of  the  mantle,  just  like  the  fibers  of  the  layer  of  cortical  association 
(see  also  Fig.  83). 

The  mantle  of  birds  is,  so  far  as  we  now  know,  not  much  more  extended 
than  that  of  reptiles.  Only  in  the  frontal  portions,  and  then  in  the  occipital 
lobe, — appearing  here  for  the  first  time, — does  it  manifest  any  essential 
progress. 

In  order  that  you  may  quite  clearly  recognize  the  development  of  the 
brain-mantle, — the  increase  of  the  cortical  area, — I  present  in  Fig.  123  a 
reptilian  brain  which  I  have  inscribed  within  the  brain  of  one  of  the  lowest 


Fig.  122. — Sagittal  section  through  the  brain  of  an  adult  ray. 


mammals:  a  marsupial.  The  reptilian  brain  is  so  inscribed  that  the  two 
Psalteria  coincide  (see  page  172). 

The  similarity  of  the  two  brains  is  at  once  apparent;  one  notes  that  the 
Gyrus  limb — cornu  Ammonis — of  the  one  corresponds  to  the  same  feature 
of  the  other;  indeed,  one  recognizes  that  the  olfactory  tract,  which  enters 
into  Ammon's  horn  anteriorly  from  the  base,  exactly  corresponds  in  the  two 
figures.  Compare  especially  Fig.  114,  where,  in  the  brain  of  the  lizard,  this 
bundle  appears  just  like  the  above.  But  this  experiment  has  not  its  sole 
significance  on  the  morphological  side.  It  should  also  show  especially  in 
what  directions  the  farthest  development  of  the  brain  proceeded,  using  the 
reptile's  as  a  starting-point.  In  the  first  place,  one  recognizes  that  from  the 
brain  of  the  reptile  to  that  of  the  marsupial  is  a  much  shorter  step  than  that 
from  the  brain  of  the  marsupial  to  the  brain  of  man. 

But  only  in  mammals  does  the  mantle  with  the  cortical  portions  become 


178  ANATOMY   OF   THE    CENTRAL    NERVOUS    SYSTEM. 

a  powerful  structure  which  leaves  the  striatum  far  behind  in  size,  and  grows 
out  over  the  posteriorly  located  interbrain  and  midbrain,  even  extending 
beyond  the  cerebellum  in  man.  Very  highly  developed  brains  show,  besides 
this  posterior  growth,  also  a  bending  of  the  posterior  half  of  the  mantle 
ventrally  (Fig.  136). 

The  most  anterior  part  of  the  hemispheres — the  frontal  lobes — make 
their  appearance  only  in  the  highest  mammal,  viz.:  man. 

From  the  great  cortical  extension  of  the  mammalian  mantle  comes  a 
great  mass  of  fibers;  others  pass  into  it.  These  fibers,  collectively  desig- 
nated the  Corona  radiata,  pass  from  the  cortex  posteriorly,  to  end  in  the 
thalamus,  cerebellum,  medulla,  and  spinal  cord.  Other  large  bundles  tra- 
verse the  hemispheres,  connecting  one  territory  of  the  mantle  with  another. 


Fig.  123. — The  brain  of  a  marsupial  (Thylacinus) ,  within  which  the  brain  of 
a  reptile  is  so  inscribed  that  the  Psalteria  coincide  (compare  Fig.  114).  (After 
Flower.) 


All  of  these  taken  together  form  under  the  cortex  a  great  mass  of  white, 
medullated  substance,  whose  extension  is  relatively  greatest  in  man;  in 
lower  mammals  it  is  only  small,  in  many — the  mouse,  for  example — it  is 
quite  unimportant. 

While  the  Corona  radiata  passes  backward,  it  courses  between  the  two 
nuclei  of  the  striatum  and  associates  itself  with  the  fibers  arising  from  them. 
The  whole  fiber-complex  is  designated  as  the  Capsula  interna.  How  the 
capsule  is  composed  of  fibers  from  the  cortex  and  the  striatum  may  be  seen 
in  Fig.  102,  which  shows  a  mammalian  brain  with  that  of  a  fish  inscribed. 

But  all  of  these  outgoing  and  incoming  fibers  lie  in  the  brain-mantle 
closely  associated  into  a  bundle  which  spreads  out  anteriorly.  If  the  cortical 
apparatus  is  disproportionately  larger,  if  it  is  more  strongly  developed  in  its 


THE  CEREBRUM  OR  PROSENCEPHALON.  179 

individual  features,  then  it  must  spread  out  over  this  smaller  radiate  bundle 
of  fibers  into  folds.  Such  brain-folds,  or  Gyri,  are  lacking  in  only  a  few 
mammals  (lissencephalic  mammals);  in  all  others  they  are  present  in 
greater  or  less  abundance  (gyr encephalic  mammals).  The  arrangement  of 
the  folds,  convolutions,  or  gyri,  which  is  constant  within  certain  limits  for 
single  animals,  depends,  indeed,  upon  two  factors:  (1)  upon  the  extension 
of  the  brain-cortex  which  the  species  in  particular  Jias  acquired  in  the  course 
of  development,  and  (2)  upon  the  relative  size  of  the  cranial  cavity,  which 
naturally  must  not  proceed  in  equal  steps  with  the  cortical  development, 
since  it  is  dependent  upon  other  factors. 

One  can,  therefore,  recognize  no  progressive  development  of  brain- 
fissuring  within  the  animal  series  or  even  within  a  single  family.  For  ex- 
ample, in  the  Monotremata  the  Ornithorhynchus  has  a  perfectly  smooth 
brain,  while  the  Echidna  has  a  richly  convoluted  one.  Even  among  the 
Primates  the  ape,  Hapale,  has  a  brain  which  is  almost  completely  free  from 
convolutions. 

Xot  only  on  the  richness  of  convolutions,  but  also  on  the  course  of  the 
convolutions,  the  two  mentioned  factors  have  an  influence.  When  the  brain- 
surface  of  man  is  better  known  to  you  it  will  be  advisable  to  cast  a  glance  at 
the  various  directions  of  the  sulci  in  the  animal  series. 

It  is  the  object  here  to  show  how,  from  modest  beginnings,  is  developed 
that  great  organ — the  Mantle — which,  as  bearer  of  the  highest  psychic  ac- 
tivity, predominates  over  the  lower  brain-centers. 

The  subject  having  now  been  developed  to  that  point,  the  comparative 
anatomical  treatment  of  the  subject  should  be  brought  to  a  close. 

If  the  foregoing  presentation  has  been  attentively  followed,  two  points 
will  not  have  escaped  the  reader,  namely:  (1)  that  in  different  classes  the 
different  brain-segments  may  be  developed  in  varying  degree;  (2)  that  there 
are  really  lowly  organized  brains  in  which  no  single  part  has  reached  a  high 
development.  Furthermore,  the  brain  and  spinal  cord  of  the  urodelate  am- 
phibians is,  in  the  main,  very  little  different  from  that  of  larval  or  embryonic 
stages  of  higher  animals.  The  medulla  and  spinal  cord,  especially,  cor- 
respond to  those  of  the  human  embryo  of  about  the  second  and  third  month. 
In  fact,  the  observation  of  tailed  amphibians — the  anura  takes  a  somewhat 
higher  rank — teaches  us  that  they  lead  a  soulless  dream-life  and  that  they 
are  capable  of  psychic  activities  hardly  recognizable  to  us  now. 

In  comparative  psychological  questions  we  still  stand  quite  in  the  be- 
ginning of  our  knowledge.  That  anatomical  investigation  can  here  usefully 
co-operate — indeed,  that  to  it  it  is  granted  to  gain  a  certain  insight  just 
where  pure  psychological  observation  is  not  yet  sufficient — has  possibly  been 
shown  in  these  chapters  in  which  the  genesis  of  the  brain  has  been  followed. 


PART  III. 


THE   SPECIAL   ANATOMY  OF  THE   MAMMALIAN 
BRAIN,  WITH  ESPECIAL  CONSIDERA- 
TION OF  THE  HUMAN  BRAIN. 


(181) 


CHAPTER    XIII. 

THE    FORM-RELATIONS    OF    THE    HUMAN    BRAIN. 

ACQUAINTED  with  the  fundamentals  which  characterize  the  central 
nervous  system  of  vertebrates,  we  will  now  give  our  attention  especially  to 
the  mammalian  brain.  Seeing,  as  you  have,  how  it  has  been  slowly  evolved 
through  a  long  series  of  transitional  forms,  it  will  certainly  be  gratifying  to 
investigate  the  entire  structure,  somewhat  more  thoroughly,  in  an  example 
o'f  the  highly  specialized  brains.  The  preceding  description  has  directed 
your  attention  principally  to  the  morphology,  and  to  some  extent  the  psycho- 
physiology,  of  the  central  nervous  system.  At  present,  however,  we  must 
attempt  to  make  good  the  demands  which  medicine,  far  advanced  as  it 
already  is  in  the  diagnosis  of  nervous  diseases,  must  necessarily  make  of  the 
physician. 

The  old  physicians  have  studied  and  described  the  human  brain  almost 
exclusively;  thus  we  have  the  best  knowledge  of  its  form-relations.  The 
numerous  investigations  on  brains  of  those  who  have  suffered  intra  vitam 
from  nervous  affections,  investigations  which  we  again  owe  almost  entirely 
to  physicians,  have  increased  our  knowledge  to  such  an  extent  that  it  is  now 
possible,  in  a  measure,  to  survey  and  describe  the  human  central  nervous 
system  more  accurately — at  least  in  its  most  important  relations. 

Although  these  chapters  are  not  intended  for  beginners,  but  for  stu- 
dents who  are  already  acquainted  in  general  with  the  grosser  anatomy  of  the 
human  brain,  it  will  not  be  entirely  superfluous  to  review  these  relations. 
These  outlines  of  the  map,  on  which  later  all  the  points  of  importance  are  to 
be  designated,  are  once  more  accurately  established  by  recapitulating  what 
has  previously  been  learned.  Guided  by  embryology,  you  certainly  will 
easily  understand  the  morphological  relations  presented  by  the  adult  organ. 

A  fresh  brain  is  laid  on  its  base.  You  will  notice  at  once  the  great 
fissure  which  separates  the  hemispheres;  and  the  fissure  of  Sylvius,  which 
arose  with  the  development  of  the  temporal  lobe.  Since  the  forebrain  has 
grown  over  most  of  the  other  parts  of  the  brain  (see  Fig.  19),  these  latter 
could  be  made  visible  posteriorly  by  raising  up  the  hemispheres  and  un- 
covering them.  It  can  also  be  accomplished  by  separating  and  partially  re- 
moving the  hemispheres.  The  second  method  is  more  advantageous,  because 
a  better  view  of  the  lateral  ventricles  and  the  corpus  striatum  is  thus  ob- 
tained. Let  us,  therefore,  proceed  in  that  manner. 

(183) 


184 


ANATOMY   OF    THE    CENTRAL    NERVOUS    SYSTEM. 


The  knife  held  horizontally  passes  simultaneously  through  both  hemi- 
spheres, and  removes  sections  two  to  three  millimeters  in  thickness.  The 
first  and  second  of  these  sections  contain  very  much  gray  cortex  and  rela- 
tively little  of  the  inclosed  white  matter;  but  even  in  the  third  section  a 
large,  white,  medullary  field  is  uncovered  in  the  middle  of  each  hemisphere. 
This  is  the  centrum  semiovale. 

In  it  run  all  the  tracts  which  pass  down  from  the  cortex  and  a  portion 
of  the  fibers  which  unite  the  various  regions  of  the  brain  with  one  another. 


Sim 


Fig.  124. — Forebrain  from  above.  The  hemispheres  have  been  removed  down 
to  the  level  of  the  corpus  callosum  (Ccl).  The  white  space  between  Ccl  and 
the  cortex  is  the  centrum  semiovale.  Lt,  Ligamentum  tectum  or  stria  longit. 
Lancisi:  a  part  of  the  cortex  which  borders  on  the  corpus  callosum.  Sim,  Striae 
longitudinales  mediales:  Iong3  white  bundles  of  fibers  which  interlace  on  the 
middle  of  the  corpus  callosum.  (After  Henle.) 


On  examining  Fig.  22  we  should  expect  that  on  farther  section  only  a  thin 
epithelial  layer  would  be  found  lying  over  the  ventricles  in  the  median  line, 
between  the  hemispheres.  This  is  not  the  case,  however.  During  a  later 
embryonic  period  dense  masses  of  fibers  have  grown  transversely  over  the 


THE    FORM-RELATIONS    OF   THE    HUMAN    BRAIN. 


185 


ventricles  from  hemisphere  to  hemisphere  (at  a,  in  Fig.  22).  For  this  reason, 
therefore,  the  ventricle  is  not  found  at  the  bottom  of  the  great  fissure,  but 
the  corpus  callosum,  as  this  mass  of  transverse  fibers  is  called.  The  corpus 
callosum  is  now  divided,  and,  after  removing  what  white  matter  still  remains 


*£T IP  • 


Fig.  125. — The  brain  opened  by  a  horizontal  section  and  viewed  from  above.    The 
two  hemispheres  are  somewhat  drawn  apart  from  one  another  posteriorly. 


186  ANATOMY    OF    THE    CENTRAL    NERVOUS    SYSTEM. 

over  each  lateral  ventricle,  it  is  cut  off  anteriorly  and  posteriorly.  It  is  then 
seen  that  it  is  united  by  its  under  surface  to  thin,  white  bundles  of  fibers, 
which,  arching  over  the  cavity  of  the  ventricle,  descend  anteriorly  and  pos- 
teriorly into  the  depth  of  the  same.  They  belong  to  the  fornix. 

The  fornix  is  a  combination  of  bundles  of  fibers  which  pass  con- 
tinually along  the  edge  of  the  hemispheres.  They  arise,  on  each  side,  from 
the  mesial  border  of  the  inferior  horn  as  the  crura  fornicis  (Fig.  125,  pos- 
terior); then  converge  over  the  posterior  portion  of  the  thalamus  and  unite 
with  one  another  above  the  ventricle  to  form  a  broad  tract:  the  corpus 
fornicis.  In  the  angle  where  they  meet  a  number  of  fibers  pass  across  them 
transversely,  thus  forming  a  triangle.  This  triangle  is  known  as  the  lyra 
Davidis,  or  psalterium.  It  lies  amder  the  posterior  end  of  the  corpus  cal- 
losum  and,  for  the  most  part,  is  united  with  this.  At  this  point,  conse- 
quently, the  corpus  callosum  lies  close  to  the  edge  of  the  hemisphere.  It 
occasionally  happens,  however,  that  the  fornix  is  situated  at  some  distance 
from  it;  a  small  cavity,  the  ventriculus  Verga,  is  then  observed  between  the 
fornix  and  corpus  callosum.  In  the  anterior  part  of  the  brain  the  corpus 
callosum  recedes  constantly  from. the  edge  of  the  hemispheres,  and  a  portion 
of  the  inner  sagittal  wall  of  the  hemisphere  remains  between  it  and  the 
ventricle.  This  portion  of  the  median  wall,  situated  below  (posterior,  in  the 
horizontal  section)  the  corpus  callosum,  is  the  septum  pellucid-urn.  That  part 
of  the  great  fissure  found  between  the  two  septi  is  called  the  ventriculus 
septi  pellucidi.  Imagine  the  corpus  callosum  removed  in  Fig.  125;  the  con- 
tinuation of  the  wall  of  the  hemisphere  into  the  septum  and  the  significance 
of  the  ventricle  are  then  evident  at  once.  This  is  not  a  true  ventricle,  but, 
as  already  stated,  only  a  portion  of  the  fissure  between  the  hemispheres 
covered  over  by  the  corpus  callosum. 

The  fornix  naturally  borders  this  portion  of  the  wall  of  the  hemisphere 
also.  It  again  divides  at  the  anterior  end  of  the  corpus  callosum  into  two 
bundles,  the  columnce  fornicis,  which  descend  in  front  of  the  thalamus  as  a 
posterior  thickening  of  each  membrane  of  the  septum  pellucidum,  and  ter- 
minate provisionally  at  the  base  of  the  brain  at  the  boundary-line  between 
the  forebrain  and  interbrain. 

The  corpus  fornicis  has  been  removed,  along  with  the  corpus  callosum, 
in  Fig.  125  and  only  the  anterior  and  posterior  portions  remain  visible. 
In  the  right,  where  the  section  passes  somewhat  deeper  through  the  white 
substance,  the  fornix  is  divided  in  that  part  known  as  the  fimbria.  It  there 
lies  near  to  its  point  of  origin,  the  cornu  Ammonis.  On  the  left  I  have 
divided  it  just  where  it  arches  over  the  surface  of  the  thalamus. 

Unite  the  points  F  and  F1  by  a  gentle  curve  passing  over  the  thalamus, 
and  the  course  of  the  fornix  is  reproduced.  It  will  also  be  clear  to  you  from 
the  accompanying  median,  longitudinal  section  through  an  embryonic  brain. 


THE    FORM-RELATIONS    OF    THE    HUMAN    BRAIN.  187 

You  observe  there  that,  arising  from  the  apex  of  the  temporal  lobe,  it  arches 
over  the  interbrain  in  a  curve  and  descends  in  front  of  this  to  the  boundary 
between  the  forebrain  and  interbrain. 

After  the  fornix,  and  the  plexus  chorioideus  attached  to  it,  is  divided 
and  cut  away,  a  view  of  the  opened  ventricles  is  obtained  (Fig.  125).  The 
unpaired  ventricle  lying  in  the  median  line  is  the  cavity  of  the  primary  fore- 
brain,  now  called  the  ventriculus  teriius.  At  its  anterior  end  the  fornix 
ascends  from  below.  Then,  on  each  side  of  the  fornix  there  is  found  a  com- 
munication of  the  ventriculus  medius  with  the  ventriculi  laterales:  the 
foramen  Monroi.  The  part  of  this  ventricle  which  lies  in  the  frontal  lobe 
is  called  the  anterior  horn,  the  part  in  the  occipital  lobe  the  posterior  horn, 
and  that  in  the  temporal  lobe  the  inferior  horn.  A  finger  could  easily  be 
introduced  into  each  of  the  horns.  The  basal  regions  of  both  hemi- 
spheres are  connected  with  one  another  by  means  of  the  commissura 


Fig.  126. — Inner  aspect  of  the  embryonic  hemisphere  shown  in  Fig.  23. 
Shows  the  inner  lower  border  of  the  hemisphere,  which  becomes  thickened  into 
the  white  medullary  line  of  the  fornix.  The  latter,  however,  only  becomes 
medullated  after  birth.  ZiciscJienhirn,  Interbrain.  Tordcrhirn,  forebrain. 
Stelle,  etc.,  Point  where  the  forebrain  and  interbrain  meet. 


anterior.  The  bundles  of  white,  medullated  fibers  composing  it  are  seen 
passing  across  in  front  of  the  pillars  of  the  fornix. 

The  nucleus  caudatus  rises  from  the  floor  of  the  lateral  ventricle.  Far- 
ther posteriorly  parts  become  visible  which  no  longer  belong  to  the  hemi- 
spheres: the  interbrain  (thalamus  opticus)  and  the  midbrain  (corpora  quadri- 
gemina).  Behind  these  is  seen  the  roof  of  the  hindbrain  (the  cerebellum). 

The  cavity  between  both  thalami,  the  ventriculus  medius,  was  at  one 
time  the  cavity  of  the  interbrain-vesicle.  It  is  closed  in  above  by  the  plicated 
plexus  chorioideus,  at  the  posterior  end  of  which  lies  the  conical  projection, 
the  corpus  pineale,  now  become  solid.  The  floor  of  the  interbrain,  which  is 
naturally  formed  in  front  by  the  embryonic  terminal  lamina,  consists  of  gray 
matter  descending  like  a  funnel  toward  the  base  of  the  brain.  This  pro- 


188  ANATOMY    OF    THE    CEXTKAL    NEEVOUS    SYSTEM. 

tuberance  is  called  the  tuber  cinereum,  its  cavity  the  infundibulum.  In  Fig. 
125  it  is  not  visible,  but  may  be  seen  in  the  median  section  shown  in  Fig. 
133  and  in  front  of  the  chiasma  (lam.  t.)  in  Fig.  135. 

The  fissure  between  the  thalamus  and  the  nucleus  caudatus  is  traversed 
by  a  long  vein,  beneath  which  is  constantly  found  a  slender  tract  of  white 
fibers:  the  stria  terminalis,  or  tcenia  semicircular  is.  Isolated  depressions 
may  be  more  or  less  distinctly  recognized  on  the  surface  of  the  thalamus. 
They  separate  from  one  another  the  elevations  which  correspond  to  the 
thalamic  ganglia. 

The  tuberculum  anterius,  the  arched  surface  of  the  nucleus  anterior 
thalami,  is  always  demonstrable.  The  line  of  division  between  a  mesial  and  a 
lateral  thalamic  nucleus  is  also  pronounced  at  times.  The  entire  thalamus  is 
covered  within  by  the  central  gray  matter,  which  is  connected  for  a  short 
distance  with  the  gray  matter  of  the  opposite  side  to  form  the  commissura 
mollis.  At  the  extreme  anterior  end  the  pillars  of  the  fornix  dip  into  this 
gray  matter.  Near  the  place  where  this  occurs  a  small  bundle  of  fibers  is 
seen  on  each  side  to  ascend  from  below,  reach  the  surface  of  the  thalamus, 
and  pass  backward  close  to  its  mesial  edge.  It  then  passes,  anteriorly  to  the 
midbrain,  for  the  most  part  into  an  elongated  body,  the  ganglion  liabenulce, 
on  the  dorsal  edge  of  the  thalamus.  The  bundle  is  called  the  tcenia  tlialami, 
and  forms  an  afferent  pathway,  passing  from  the  olfactory  apparatus  at  the 
base  of  the  brain  to  the  interbrain. 

A  part  of  the  tsenia,  receiving  other  fibers  on  its  way,  passes  farther 
backward  posterior  to  the  ganglion  habenulae,  and  then  runs  to  the  other 
side  directly  in  front  of  the  pineal  body.  The  portion  between  the  ganglion 
and  the  pineal  body  is  called  the  pedunculus  conarii,  because  the  body 
appears  to  rest  on  it. 

The  decussation  of  the  bundles  lying  just  in  front  of  the  epiphysis  is 
designated  as  the  commissura  habenularum.  This  decussation  lies  directly 
dorsal  and  anterior  to  the  commissura  posterior,  from  which  in  most  cases  it 
is  not  separated  at  all  (see  Fig.  144  also). 

The  gray  mass  of  the  thalamus  is  overlaid  by  white  fibers,  the  stratum 
zonale,  which,  in  part,  pass  into  the  optic  nerve.  An  enlargement  of  the 
posterior  portion  of  the  thalamus,  the  pulvinar,  forms  the  chief  point  of 
origin  of  these  nerves.  The  largest  part  of  the  optic  nerve  disappears  in  this 
ganglion  and  in  a  protuberance  which  lies  on  its  under  side:  the  corpus 
geniculatum  laterale. 

The  tracts  of  nerves  from  the  hemispheres,  which  were  situated  deep 
down  between  them  and  the  interbrain,  emerge  in  great  part  from  the  cere- 
bral mass  posteriorly  to  the  interbrain,  and  then  lie  exposed  as  two  thick 
strands  on  the  under  surface  of  the  midbrain.  Taken  together,  they  are 
called  the  crura  of  the  brain,  or  the  pedunculi  cerebri. 


THE    FORM-RELATIONS    OF   THE    HUMAN    BRAIN. 


189 


The  roof  of  the  midbrain  commences  behind  the  pineal  body.  The 
commissura  posterior,  the  crura  of  which  pass  backward  through  the  mid- 
brain,  is  regarded  as  the  most  anterior  portion  of  its  roof.  The  corpora 
quadrigemina,  appearing  just  behind  this  commissura,  will  be  considered 
more  closely  later. 

Only  the  mesial  portion  of  the  corpus  striatum,  the  nucleus  caudatus, 
is  visible  if  the  brain  is  opened,  as  has  just  been  done,  from  above  down- 
ward. The  lateral  portion,  the  nucleus  lentiformis,  lies  deeper  and  is 


Fig.  127. — Frontal  section  through  the  brain  of  the  adult.    Explanation  in  the  text. 


covered  by  the  medullary  masses  passing  over  it  into  the  capsula  interna. 
It  could  be  exposed  by  opening  downward  outside  of  the  nucleus  caudatus. 
A  better  idea  of  its  form  is  obtained,  however,  by  making  a  frontal  section 
transversely  through  the  entire  brain  at  the  point  in  Fig.  125  where  the 
thalamus  begins,  just  behind  the  thickest  part  (caput)  of  the  nucleus  cau- 
datus; that  is  to  say,  just  posteriorly  to  the  ascending  pillars  of  the  fornix. 
It  is  not  very  difficult  to  understand  the  section  (Fig.  127)  made  in  this 
manner,  if  the  relations  shown  in  Fig.  22  are  borne  in  mind.  The  wall  of 


190  ANATOMY   OF   THE    CENTRAL    NERVOUS    SYSTEM. 

the  brain  is  decidedly  thicker  than  during  the  foetal  period,  but  the  corpus 
striatum  still  projects  from  the  floor  into  the  cavity  of  the  ventricle,  as  in 
that  section.  The  outer  fissure  is  now  obliterated,  since  the  coronal  fibers 
from  the  cortex  have  increased  in  late  embryonic  life.  At  the  bottom  of  the 
great  fissure  the  ventricle  is  seen  to  be  covered  by  the  dense  transverse  fibers 
of  the  corpus  callosum.  To  these  there  ascend  from  below  the  two  pillars  of 
the  fornix,  leaving  the  ventriculus  septi  pellucidi  free  between  the  thin  mem- 
branes of  the  septum  pellucidum.  They  project  freely  into  a  cavity:  the  lat- 
eral ventricle.  This  cavity  is  bounded  without  by  the  corpus  striatum.  Just 
here  it  may  be  beautifully  seen  how  the  corpus  striatum  is  penetrated,  and 
apparently  divided  into  two  ganglia,  by  the  thick  masses  of  fibers  forming 
the  internal  capsule.  In  the  lenticular  nucleus — that  is  to  say,  in  the  outer 
part  of  the  corpus  striatum — three  divisions  are  easily  distinguished.  Only 
the  outer  one  of  the  three  parts,  the  putamen  (shaded  heavily  in  Fig.  127), 
is  regarded  in  common  with  the  nucleus  caudatus  as  a  source  of  fibers.  The 
significance  of  the  two  inner  parts,  globus  pallidus,  is  not  clear  as  yet.  Some- 
times the  globus  pallidus  consists  of  three  or  more  divisions.  Externally  to 
the  lenticular  nucleus  there  lies  a  thin,  gray  mass  in  the  wall  of  the  hemi- 
sphere known  as  the  daustrum.  The  space  between  it  and  the  lenticular 
nucleus  is  called  the  capsula  externa.  Still  farther  out  lies  the  cortex  of  the 
island  of  Reil.  The  gray  mass  in  the  floor  of  the  middle  ventricle  belongs 
to  the  wall  of  the  infundibulum,  the  tuber  cinereum.  With  its  continuations, 
it  is  spoken  of  as  the  central  gray  matter  of  the  ventricle.  At  the  point  where 
this  central  gray  matter  and  the  cortex  of  the  temporal  lobe  are  continuous 
with  one  another  there  lies  a  large,  roundish  nucleus:  the  nucleus  amygdalae. 
It  probably  stands  in  some  relation  to  the  terminal  apparatus  of  the  olfactory 
nerve.  From  the  neighborhood  of  the  nucleus  amygdala?,  probably  from  the 
nucleus  itself,  there  arises  a  portion  of  those  bundles  of  fibers  which  pass  as 
the  stria  cornea  between  the  thalamus  and  the  nucleus  caudatus. 

We  know  from  comparative  anatomical  investigations  that  the  space  between 
the  infundibulum  and  the  nucleus  amygdalae,  shown  in  horizontal  section  in  the 
illustration  and  included  with  the  central  gray  matter,  is  a  cortical  region  which  is 
very  much  atrophied  in  man.  It  is  designated  as  the  olfactory  field. 

Between  the  pillars  of  the  fornix  the  anterior  commissure  is  seen  (Fig. 
125).  Its  fibers  curve  backward  as  they  pass  through  the  corpus  striatum. 
Thus  it  happens  that  we  again  meet  with  them  in  transverse  section,  just 
below  the  outer  part  of  the  lenticular  nucleus  (Fig.  127,  below  and  to  the 
left). 

I  cannot  urge  you  too  strongly  to  look  up  in  the  fresh  brain  all  the 
structures  just  mentioned  and  to  become  acquainted  with  their  relations  by 
making  preparations  of  your  own.  Descriptions  and  illustrations  will  prob- 


THE    FORM-RELATIONS    OF    THE    HUMAN    BRAIN.  191 

ably  give  you  a  good  idea  of  them,  but  they  can  never  supply  what  is  to  be 
gained  by  the  study  of  the  brain  itself. 

We  will  now  consider  the  convolutions  and  fissures  of  the  surface  of 
the  cerebrum. 

It  is  not  so  very  long  ago  that  anatomists  manifested  little  interest,  and 
physicians  none  at  all,  in  the  study  of  the  conformation  of  the  cerebral 
surface.  Neither  is  it  so  very  long  since  order  was  brought  out  of  the  seem- 
ing chaos  of  the  convolutions,  and  clear  and  accurate  illustrations  took  the 
place  of  those  old  plates  concerning  which  an  author  pertinently  remarked 
that  they  resembled  a  dish  of  macaroni  more  than  the  brain.  Interest  was 
first  actively  stimulated  in  regard  to  the  human  brain  only  after  physiology, 
followed  shortly  by  pathology,  had  shown  how  differently  irritations,  extir- 
pations, and  diseases  appear  according  as  they  involve  this  or  that  convolu- 
tion of  the  hemisphere. 

It  will  be  impossible  to  become  as  thoroughly  acquainted  with  the  course 
of  the  convolutions  as  is  desired,  merely  from  descriptions  and  diagrams. 


Fig.  128. — Brain  of  a  human  foetus  of  the  thirteenth  week. 

Take  a  brain,  therefore,  and,  following  my  description,  trace  out  for  your- 
selves sulcus  after  sulcus  and  gyrus  after  gyrus. 

The  hemispheres,  primarily  lens-shaped,  grow  out  anteriorly  and  pos- 
teriorly. In  the  middle  only,  at  a  point  corresponding  to  the  corpus  striatum 
within,  the  wall  fails  to  follow  this  expansion  as  rapidly,  and  thus  gradually 
becomes  more  deeply  situated.  The  flat  depression,  which  in  this  manner 
arises  on  the  stem  of  the  hemisphere,  is  called  the  fossa  Sylvii,  and  that  part 
which  lies  in  the  depression,  the  lobe  of  the  stem,  or  the  insula  Reilii.  The 
island  is,  therefore,  that  part  of  the  cortex  which  adjoins  the  ganglia  of  the 
cerebrum  from  without.  At  first  it  is  entirely  uncovered,  but  later  is  more 
and  more  concealed  by  the  expanding  hemisphere  overlapping  it. 

This  depression  is  easily  found  on  the  adult  brain,  likewise  its  posterior 
continuation,  the  largest  of  the  brain-fissures:  the  fissura  Sylvii.  If  the 
fissure  is  drawn  apart,  the  island  of  Eeil  is  discovered  at  the  bottom  tra- 
versed by  several  perpendicular  and  oblique  sulci.  Even  in  the  fifth  month 
of  pregnancy  two  divisions  of  the  Sylvian  fissure,  an  anterior  and  posterior, 


192 


ANATOMY    OF    THE    CENTRAL    NERVOUS    SYSTEM. 


are  distinctly  to  be  seen.  All  the  rest  of  the  brain  is  still  smooth  (compare 
Fig.  23). 

From  this  developmental  period  on,  fissures  (suki)  are  formed  on  the 
surface  of  the  hemisphere  by  local  elevations  (gyri)  of  the  cortex.  These 
sulci  and  gyri  increase  more  and  more  in  the  later  months  of  fetal  life,  until, 
at  the  time  of  birth,  almost  all  the  fissures  and  convolutions  which  the  adult 
brain  will  possess  are  clearly  defined. 

The  following  drawings,  purely  diagrammatic,  may  serve  as  guides  in 
the  study  of  the  surface  of  the  hemispheres.  Only  the  more  important 
and  constant  fissures  and  convolutions  are  therein  indicated.  A  simple 


Gca 


Fig.  129. — The  left  hemisphere  with  the  fissura  Sylvii  drawn  apart  in  order 
to  show  the  insula  (In).  Sc,  Sulcus  centralis.  gca,  gcp,  Gyrus  centralis  anterior 
and  posterior.  Fop,  Fissura  parieto-occipitalis.  (After  Henle.) 


diagram  is  more  easily  remembered  than  representations  of  the  surface  of  the 
brain,  which  reproduce  the  smaller  gyri  and  shallower  sulci,  all  of  which 
are  inconstant,  alongside  of  those  which  are  more  pronounced  and  constant. 
First  locate  the  fissure  of  Sylvius.  It  separates  the  greatest  part  of  the 
temporal  lobe  from  the  rest  of  the  brain.  A  long  posterior  limb  and  one  or 
two  short  anterior  branches,  which  are  directed  upward,  are  distinguished 
on  it.  The  mass  of  the  brain  which  lies  at  the  point  where  these  join  one 
another  covers  the  island  of  Eeil  and  is  called  the  operculum.  If  those  parts 
of  the  brain  which  surround  the  fissure  of  Sylvius  are  separated  from  one 


THE    FORil-EELATIOXS    OF    THE    HUMAX    BRAIN. 


193 


another,  as  has  been  done  in  the  preparation  shown  in  Fig.  129,  the  island 
lies  in  full  view.  The  island  is  then  seen  to  be  divided  into  two  small  lobules 
by  means  of  a  deep  fissure,  the  sulcus  centralis  insulce,  which  passes  obliquely 
upward  and  backward  from  below  and  in  front.  Several,  almost  perpendicu- 
lar, sulci  divide  the  anterior  broader  lobule  into  three  or  four  gyri  breves 
insula3.  The  posterior  lobule  is  really  nothing  but  a  single,  longer  gyrus: 
the  gyrus  longus.  It  borders  directly  on  the  temporal  lobe.  An  important 
fissure,  the  sulcus  centralis  or  central  fissure,  begins  in  the  operculum,  and 
ascends  from  there  to  the  median  edge  of  the  hemisphere,  which  it  frequently 
incises.  At  the  bottom  of  this  fissure  a  small  annectant  gyrus  not  infre- 
quently divides  it  into  a  superior  and  inferior  portion.  Eecent  surgical 


Fig.  130. — Lateral  aspect  of  the  brain.     The  gyri  and  lobuli  are  designated  by 
Roman  letters,  the  sulci  and  fissurae  by  italics. 


operations,  as  well  as  the  knowledge  gained  from  physiological  studies,  have 
made  it  desirable  to  divide  the  fissure  in  parts.  The  two  genua,  the  superior 
genu  and  the  inferior  genu  of  the  central  sulcus,  respectively  indicated  in 
the  diagram  by  an  asterisk,  serve  as  such  points  of  division.  Locate  the 
fissure  in  Fig.  130.  This  central  sulcus  separates  the  lolus  frontalis  from 
the  lolus  parietalis.  All  that  lies  below  the  Sylvian  fissure  is  called  the 
lobus  temporalis.  In  front  of  the  sulcus  centralis  lies  the  anterior  central 
gyrus,1  behind  it  the  posterior  central  gyrus.2  The  region  in  front  of  the 


Circonvolution  frontale  ascendente  of  the  French  writers. 
Circonvolution  parietale  ascendente  of  the  French  writers. 

13 


194  ANATOMY    OF    THE    CENTBAL    NTERVOUS    SYSTEM. 

anterior  central  convolution,  the  frontal  lobe,  is  divided  by  two  fissures,  the 
superior  and  inferior  frontal  sulci,  into  three  gyri:  the  superior,  middle,  and 
inferior  frontal  gyri.  These  convolutions  are  not  always  sharply  separated 
from  one  another  along  the  entire  extent  of  the  frontal  lobe,  inasmuch  as 
the  fissures  are  frequently  interrupted  after  a  short  course  by  annectant  gyri. 
These  three  divisions  of  the  frontal  lobe,  lying  above  one  another,  are  readily 
found  on  all  brains.  It  will  probably  be  observed  also  that  they  are  con- 
nected with  the  anterior  central  convolution  by  means  of  several  annectant 
gyri.  From  the  central  convolution,  they  are  separated  by  a  fissure,  the 
sulcus  prcecentralis,  of  variable  length  and  depth.  Besides  an  inferior,  more 
constant,  part,  this  sulcus  has  a  shorter  superior  part,  which  is  demonstrable 
at  times.  According  to  the  investigations  of  Schnopfhagen,  the  relation 
here  shown  diagrammatically  in  Fig.  130  is  said  to  be  the  most  common  one. 

On  the  broad  middle  convolution  of  the  frontal  lobe  there  has  lately  been  dis- 
tinguished a  mesial,  from  a  lateral,  division.  The  inferior  frontal  convolution  is  in- 
cised by  the  two  short  anterior  branches  of  the  fissure  of  Sylvius.  They  join  the 
main  horizontal  limb  in  the  form  of  a  V.  This  V-shaped  region  is  the  portion  of 
the  gyrus  designated  as  the  pars  opercularis.  Considerable  variations  occur  at  this 
point,  which  depend  on  the  degree  of  intellectual  development  of  the  individual. 
That  portion  is  especially  subject  to  variations  which  lies  between  the  posterior  arm 
of  the  V  and  the  anterior  central  gyrus:  the  pes  of  the  inferior  frontal  convolution. 
It  is  a  simple  convolution,  which  often  shows  indentations,  extensions,  etc.  On  the 
brain  of  Gambetta,  a  famous  orator,  it  consisted  of  a  double  convolution  on  the  left 
side. 

The  brain  of  the  anthropoid  apes  is  surprisingly  similar,  as  regards  convolu- 
tions, to  that  of  man.  That  which  especially  distinguishes  it  from  that  of  man,  how- 
ever, is  the  development  of  the  frontal  convolutions.  The  superior  and  middle  gyri 
are  always  very  much  shorter,  and  only  rudiments  of  the  inferior  gyrus  are  demon- 
strable. It  is  highly  probable  that  this  is  the  anatomical  expression  of  inferior  in- 
telligence, particularly  of  the  utterly  undeveloped  faculty  of  articulate  speech.  As 
we  probably  owe  the  perfection  of  our  intelligence  to  our  faculty  of  speech — not  as 
individuals,  but  as  a  race — the  reason  for  the  inferior  development  of  the  entire 
frontal  lobe  in  apes  may,  perhaps,  be  found  in  the  imperfect  development  of  the 
inferior  frontal  gyrus. 

The  temporal  lobe  is  traversed  by  several  sulci,  which  run  parallel  with 
the  fissura  Sylvii,  and,  more  or  less  distinctly  separate  from  one  another,  a 
superior,  middle,  and  inferior  temporal  gyrus.  In  most  cases  only  the  first 
two  of  these  gyri  are  plainly  distinguishable  throughout  their  entire  extent. 

Now  observe  the  region  behind  the  central  fissure  and  above  the  tem- 
poral lobe;  it  is  called  the  parietal  lobe.  It  is  divided  into  a  superior  and 
an  inferior  parietal  lobule  by  the  sulcus  inter parietalis,  which  arches  around 
the  end  of  the  fissure  of  Sylvius  and  the  first  temporal  sulcus.  Throughout 
most  of  its  extent,  the  superior  lobule  is  not  separated  from  the  posterior 
central  gyrus,  unless,  as  often  happens,  a  branch  of  the  sulcus  interparietalis 


THE    FORM-RELATIONS    OF    THE    HUMAN    BRAIN. 


195 


ascends  toward  the  edge  of  the  hemisphere  and  thus  considerably  interrupts 
the  continuity. 

This  branch,  the  fissura  retrocentralis  superior,  often  occurs  independent  of 
the  interparietal  fissure.  The  interparietal  fissure  allows  the  recognition  of  three 
divisions,  which  are  occasionally  separate  from  one  another.  The  anterior  division  is 
called  the  flssura  retrocentralis  inferior,  the  posterior  the  sulcus  occipitalis  ante- 
terior  or  perpendicularis. 

The  portion  of  the  inferior  parietal  lobule  which  surrounds  the  end  of 
the  fissure  of  Sylvius  is  called  the  gyrus  marginalis.  The  part  that  lies  just 
back  of  this  and  arches  around  the  superior  temporal  sulcus  is  the  gyrus 


Fig.  131. — Lateral  aspect  of  brain. 


angularis.  The  former  gyrus  is  at  once  observed  on  every  brain;  the  latter 
must  be  searched  for  with  some  diligence.  It  is  found  in  the  space  bounded 
above  by  the  interparietal  fissure  and  below  by  the  superior  temporal  sulcus; 
that  is  to  say,  its  end.  Its  posterior  part,  indeed,  just  surrounds  the  end  of 
this  sulcus.  The  region  of  the  gyrus  angularis  is  an  important  one,  and  it 
is  therefore  advantageous  to  be  able  to  locate  and  bound  it  well.  The  small 
gyrus  directly  posterior  to  it  is  the  gyrus  parietalis  posterior. 

The  occipital  lobe  is  not  so  uniformly  fissured  in  all  brains  that  the 
convolutions  described  by  writers  as  superior,  middle,  and  inferior  may  be 
easily  identified  without  elaboration.  It  is  commonly  separated  from  the 
parietal  lobe  by  the  anterior  occipital  sulcus,  which  passes  vertically  down- 


196  ANATOMY   OF    THE    CENTRAL   NEKVOUS    SYSTEM. 

ward  behind  the  lobulus  parietalis  inferior.  One  or  two  small  sulci,  placed 
somewhat  horizontally,  separate  the  small  gyri  from  one  another. 

When  all  of  these  fissures  and  convolutions  have  been  found,  cut  the 
brain  in  two  along  the  line  of  the  great  longitudinal  fissure,  and  study  the 
mesial  side  of  the  hemisphere. 

The  most  important  parts  of  the  mesial  wall  of  the  hemisphere  are 
already  familiar  to  you  from  the  study  of  their  embryology  in  the  second 
chapter.  It  was  there  learned  that  the  edge  of  the  hemisphere,  thickened 
to  form  the  fornix,  follows  in  curved  line  the  hemisphere,  which  grows  out 
posteriorly  and  inferiorly;  that  anteriorly,  where  the  corpus  callosum  passes 
across  from  one  hemisphere  to  the  other,  the  portion  of  the  inner  wall  which 
lies  between  the  fornix  and  the  corpus  callosum  remains  as  the  septum 
pellucidum. 

From  its  embryology,  the  section  previously  made  through  the  brain  of 


Fig.  132. — Inner  aspect  of  the  embryonic  hemisphere  shown  in  Fig.  23.  It 
shows  the  inner,  inferior  edge  of  the  hemisphere,  which  becomes  thickened  to 
form  the  white,  medullated  line  of  the  fornix.  This,  however,  becomes  medullated 
after  birth  only.  Zicischenhirn,  Interbrain.  Yorderhirn,  forebrain.  Stelle,  etc., 
Place  where  forebrain  and  interbrain  meet. 


the  adult  is  easily  understood.  In  the  preparation  from  which  the  accom- 
panying illustration  was  made  (Fig.  133),  as  well  as  on  the  embryonic  brain 
now  again  demonstrated  (Fig.  132),  all  the  parts  that  lie  behind  the  middle 
of  the  thalamus  have  been  cut  away,  because  they  conceal  the  under  surface 
of  the  temporal  lobe  and  prevent  us  from  following  the  fornix. 

The  interbrain — that  is,  its  lateral  wall,  the  thalamus  opticus — is  there- 
fore now  observed  in  the  center  on  the  longitudinal  section.  The  margin  of 
the  hemisphere,  thickened  to  form  a  white,  medullary  band,  the  fornix, 
passes  in  a  curved  line  along  the  boundary  between  the  interbrain  and  the 
cerebrum.  It  first  appears  near  the  base  of  the  brain  in  the  gray  matter 
behind  the  lamina  terminalis;  ascends  dorsally  as  the  columna  fornicis; 


THE    FORM-RELATIONS    OF   THE    HUMAN   BRAIN. 


197 


then  accompanies  the  margin  of  the  hemisphere  still  farther;   curves  with 
it  into  the  temporal  lobe,  and  ends  only  at  its  apex. 

The  horizontal  mass  of  transversely-divided  fibers  above  the  fornix 
belongs  to  the  corpus  callosum.  On  this  there  is  distinguished  anteriorly 
the  genu,  posteriorly  the  splenium,  and  between  the  two  the  ~body.  Between 
the  corpus  callosum  and  the  fornix  lies  the  triangular  field  of  the  septum. 
Moreover,  just  in  front  of  and  below  the  fornix  the  commissura  anterior  is 
seen  in  transverse  section;  it  lies  in  the  middle  of  the  lamina  terminalis. 
The  lamina  terminalis  then  continues  ventrally  into  the  floor  of  the  inter- 
brain,  and  is  here  somewhat  infolded  by  the  chiasma — also  cut  transversely. 


Fig.  133. — Longitudinal  section  through  the  middle  of  an  adult  brain.  The 
posterior  portion  of  the  thalamus,  the  crura  cerebri,  etc.,  have  been  removed,  in 
order  to  expose  the  inner  surface  of  the  temporal  lobe. 


These  structures,  in  part  membranous,  have  been  purposely  left  intact  in 
the  preparation  in  order  that  the  floor  of  the  middle  ventricle  might  be 
seen  once  more.  The  posterior  wall — the  infundibulum  and  its  transition 
into  the  ventral  region  of  the  midbrain,  the  prominence  of  the  tegmentum — 
has  also  been  left  in  place.  In  your  own  preparations,  however,  remove  all  of 
these  gray  parts  and  observe  how  the  fornix  terminates  behind  the  region 
designated  as  uncus. 

The  portion  of  the  wall  of  the  hemisphere  which  lies  above  the  corpus 
callosum  is  traversed  by  few  and  rather  constant  fissures. 

First  of  all,  the  sulcus  cinguli  runs  parallel  with  the  corpus  callosum. 


198  ANATOMY    OF    THE    CENTRAL    NERVOUS    SYSTEM. 

Posteriorly,  it  turns  upward  to  the  edge  of  the  hemisphere  and  there  ends 
in  a  small  incision  behind  the  posterior  central  gyrus. 

The  sulcus  cinguli — which  also  bears  the  names  of  sulcus  calloso-marginalis, 
marginal  fissure,  fissura  limbica,  and  fissura  splenialis — consists,  properly  speak- 
ing, of  three  parts  lying  one  behind  the  other.  Not  infrequently  these  are  really 
separate  sulci. 

That  which  lies  above  and  in  front  of  this  sulcus  cinguli  is  regarded 
as  belonging  to  the  superior  frontal  convolution;  the  convolution  lying  be- 
tween it  and  the  corpus  callosum  is  called  the  gyrus  fornicatus.  A  glance  at 
a  specimen  or  the  illustration  shows  that  the  gyrus  fornicatus  widens  out 
superiorly  in  its  posterior  part  and  passes  directly  over  the  edge  of  the  hemi- 
sphere into  the  lobulus  parietalis  superior.  This  widened  portion  is  called 
the  prcecuneus.  Directly  in  front  of  the  prascuneus  lies  a  part  of  the  cortex 
which  adjoins  both  central  gyri  without  and  connects  these  with  one  an- 
other. It  is  called  the  paracentral  lobule. 

The  praecuneus  is  terminated  posteriorly  by  a  deeply-incised  fissure, — 
the  fissura  parieto-occipitalis, — which  always  extends  for  some  distance  over 
upon  the  outer  surface  of  the  hemisphere.  This  parieto-occipital  fissure 
frequently  passes  very  far  beyond  the  inner  surface  and  runs  out  over  the 
hemisphere  externally  as  a  deep  vertical  fissure,  the  fissura  perpendicularis 
ext.  This  is  very  frequently  the  case  in  the  brains  of  idiots.  In  almost 
all  simian  brains  a  broad  fissure  begins  in  the  parieto-occipital  fissure  (or  just 
behind  it,  Ziehen  and  Kukenthal),  which  passes  downward  over  the  greater 
part  of  the  lateral  surface  of  the  hemisphere  and  in  a  very  striking  manner 
separates  the  parietal  from  the  temporal  lobe.  -It  is  called  the  simian  fissure, 
or  "Affenspalte." 

The  fissura  calcarina  joins  the  parieto-occipital  fissure  at  an  acute 
angle.  This  fissure  lies  exactly  in  the  outer  wall  of  the  posterior  horn  of  the 
lateral  ventricle.  The  wall  of  the  brain  infolded  by  it  is  indicated  within  the 
posterior  horn  by  an  elongated  prominence  known  as  the  calcar  avis.  The 
triangular  cortical  area  inclosed  by  the  fissura  parieto-occipitalis  and  the 
fissura  calcarina  is  called  the  cuneus.  If  the.  vertex  of  this  triangle  is  now 
located,  several  small  annectant  gyri,  superficially  or  deeply  situated,  are 
found  connecting  it  with  the  end  of  the  gyrus  fornicatus,  which  passes  by 
in  front  of  the  vertex  of  the  cuneus.  Notice  this  comparatively  narrow  part 
of  the  gyrus  fornicatus:  the  hilus.  It  is  seen  to  continue  as  a  rapidly  widen- 
ing convolution  to  the  apex  of  the  temporal  lobe,  where  it  ends  in  a  hook- 
like  process:  the  uncus,  or  gyrus  uncinatus. 

This  convolution  consequently  surrounds  the  entire  margin  of  the 
hemisphere.  In  fact,  it  is  called  the  marginal  convolution;  in  which  case 
only  the  anterior  portion  receives  the  name  of  gyrus  fornicatus,  while  the 


THE    FORM-RELATIONS    OF   THE    HUMAN    BRAIN. 


199 


name  of  gyrus  hippocampi  is  given  to  the  part  lying  posterior  and  ventral. 
Posteriorly,  as  is  well  seen  in  the  figure,  a  small,  longish  convolution  of  the 
occipital  lobe  joins  the  gyrus  hippocampi;  it  is  called  the  gyrus  lingualis. 

As  has  previously  been  shown,  the  fornix  forms  the  edge  of  the  hemi- 
sphere. The  first  portion  of  the  wall  of  the  brain  succeeding  this  is  the 
above-mentioned  gyrus  hippocampi,  which  is,  therefore,  adjacent  to  the 
fornix.  Externally  to  it  lies  the  cavity  of  the  ventricle:  the  inferior  horn. 

The  ventricle  is  separated  at  this  place  from  the  cranial  cavity  by  a 
thin,  vascular  membrane  only, — the  continuation  of  the  plexus  chorioideus, 
— which  is  attached  to  the  fornix  throughout  its  entire  extent. 

The  gyrus  hippocampi  is  covered  by  cortical  matter,  but  the  cortex 
ceases  on  the  side  toward  the  inferior  horn;  and,  close  to  the  ventricle,  the 
white  medullary  substance,  no  longer  covered  by  gray  matter  as  on  the  entire 


Fig.    134a.  Fig.  1346.  Fig.  134c. 

Fig.  134a.    Fig.  1346.    Fig.  134c.     Unterhorn,  Inferior  horn. 


outer  surface  of  the  brain,  lies  exposed.  This  medullary  substance — a  long, 
white  stripe,  which  is  directly  continuous  with  the  fornix  above — is  called 
the  fimbria  (Fig.  133). 

The  marginal  convolution  is  pushed  by  a  fissure  of  its  outer  surface — 
the  fissura  hippocampi — into  the  cavity  of  the  inferior  horn.  The  elevation 
thus  produced  along  the  entire  floor  of  the  inferior  horn  has  borne  for  cent- 
uries the  name  of  cornu  Ammonis,  or  pes  hippocampi  major. 

Owing  to  the  fact  that  the  cortex  of  the  gyrus  hippocampi  is  also  infolded  by 
that  fissure  before  the  cortex  entirely  ceases  and  leaves  the  medullary  substance  ex- 
posed, there  is  presented  a  peculiar,  somewhat  complicated  section,  if  the  gyrus  is 
cut  transversely.  On  other  parts  of  the  brain  the  cortex  covers  the  surface  con- 
tinuously, as  is  shown  in  Fig.  134a;  it  ceases,  however,  close  to  the  ventricle  at 
the  marginal  infolding,  and  leaves  exposed  a  white,  somewhat  curved  border,  the 


200  ANATOMY    OF    THE    CENTRAL   NERVOUS    SYSTEM. 

fimbria.  Fig.  134c  is  intended  to  shoAv  this  and  the  infolding  which  the  cortex  un- 
dergoes before  it  ends.  Between  the  gyrus  hippocampi  and  the  free,  medullary  edge 
of  the  hemisphere  (fimbria — fornix),  there  still  lies,  however,  a  small  convolution, 
which  has  purposely  not  been  mentioned  heretofore.  It  passes  downward  from  the  end 
of  the  corpus  callosum  to  the  apex  of  the  temporal  lobe,  and  therefore  takes  part  in 
the  configuration  of  the  cornu  Ammonis  also.  Locate  this  narrow  gyrus,  designated 
as  the  gyrus  dentatus  or  fascia  dentata,  on  the  sagittal  section  previously  demon- 
strated, in  order  to  make  its  relation  to  the  fornix  and  the  gyrus  hippocampi  per- 
fectly clear.  It  lies,  as  is  there  seen,  just  in  front  of  the  inrolling  of  the  gyrus 
hippocampi,  produced  by  the  similarly  named  fissure.  A  cross-section  of  the  gyrus 
dentatus  is,  therefore,  not  represented  by  Fig.  1346,  but  more  correctly  by  Fig.  134c. 

The  cornu  Ammonis  is,  therefore,  the  bulging  that  arises  in  the  ventricle  through 
the  infolding  of  the  gyrus  hippocampi  by  the  fissura  hippocampi.  The  complicated 
appearance  of  the  cornu  Ammonis,  when  seen  in  transverse  section,  is  due  to  the 
fact  that  the  cortex  of  the  gyrus  ceases  just  at  this  place,  and  that  the  fimbria  and 
gyrus  dentatus  run  along  over  this  infolding. 

The  relation  of  the  gyrus  hippocampi  to  the  inferior  horn  of  the  lateral  ven- 
tricle becomes  clearest,  if  their  cross-sections  are  traced  in  the  large  sections  of  the 
brain  reproduced  in  Figs.  175,  185,  186,  and  187. 

The  gyrus  fornicatus  and  its  continuation,  the  gyrus  hippocampi,  are  formed 
rather  early  in  the  embryo.  Dorsal  to  the  margin  of  the  hemisphere  (arch  of  the 
fornix)  there  appears  in  all  mammals  a  fissure  which,  running  parallel  with  the 
fornix,  passes  down  with  it  into  the  temporal  lobe.  It  is  called  the  marginal  fissure, 
or  fissura  limMca,  and  the  gyrus  left  between  it  and  the  fornix,  the  marginal  con- 
volution. The  fibers  of  the  corpus  callosum  pass  between  this  gyrus  and  the  fornix 
in  the  more  anterior  region  of  the  brain,  and  the  convolution  is  there  known  as  the 
gyrus  fornicatus.  The  more  posterior  portion  of  the  marginal  convolution,  however, 
— the  portion  designated  as  the  gyrus  hippocampi, — borders  almost  directly  on  the 
fornix.  In  most  mammals  the  corpus  callosum  and  the  gyrus  fornicatus  are  very 
short. 

If  the  upper  surface  of  the  corpus  callosum  is  again  examined,  a  thin, 
gray,  longitudinal  line  will  be  seen  upon  it  on  each  side  (Fig.  124,  Lt).  That 
line — the  stria  longitudinalis  Lancisi — is  the  continuation  of  the  gyrus  den- 
tatus: a  convolution  atrophied  even  in  the  cornu  Ammonis. 

At  the  posterior  end  of  the  corpus  callosum  a  short  convolution  is  some- 
times seen  passing  in  a  direction  toward  the  fornix,  with  which  it  unites. 
It  is  the  gyrus  callosus,  which  occurs  in  man  as  a  very  atrophic  structure 
only,  and  is  not  at  all  constant. 

Find  the  gyrus  uncinatus  on  the  fresh  brain  internal  to  the  apex  of  the 
temporal  lobe,  and  from  there  follow  the  gyrus  hippocampi  upward.  Then 
find  the  arch  of  the  fornix,  which  is  easily  done,  above  the  posterior  portion 
of  the  thalamus,  and  note  that  it  passes  over  into  the  fimbria,  which  is 
visible  as  a  white,  medullary  line  almost  to  the  apex  of  the  cornu  Ammonis. 
Finalty,  make  a  frontal  section,  which  will  show  the  relation  of  the  structures 
named  to  the  inferior  horn. 

On  the  base  of  the  brain  only  a  few  important  fissures  are  found  in  addi- 


THE    FORM-RELATIONS    OF   THE    HUMAN   BRAIN.  201 

tion  to  the  fissura  hippocampi,  which  really  belongs  to  the  mesial  surface. 
On  the  under  surface  of  the  frontal  lobe  lie  the  sulci  orbitales  and  olfactorii. 
The  convolutions  between  them,  regarded  as  continuations  of  the  frontal 
gyri,  are  designated  by  the  names  of  those  frontal  gyri  with  which  they  are 
respectively  continuous. 

The  cortex  of  the  basal  surface  of  the  frontal  lobe  borders  on  that  gray  matter 
at  the  base  of  the  brain  which  belongs  to  the  olfactory  apparatus.  We  shall  have 
occasion  to  consider  this  gray  matter  later.  Two  small  elevations  situated  near  the 
median  line  and  extending  out  from  this  gray  matter  dorsally,  the  gyrus  rectus  and 
the  gyrus  subcallosus  lying  behind  this,  belong,  perhaps,  to  the  olfactory  apparatus. 
At  all  events^  the  latter  of  the  two  gyri  arises  from  the  outfolding  produced  by  a 
bundle  of  fibers  passing  along  under  it  in  this  situation,  which  bundle  passes  from 
the  terminations  of  the  olfactory  radiation  up  over  the  septum  into  the  fornix.  It 
is  that  very  bundle  to  which,  in  the  lower  vertebrates,  I  thought  it  necessary  to 
attribute  so  great  significance  for  the  interpretation  of  the  mesial  cortex  of  the  brain. 
See  Figs.  76  and  100:  Tr.  cortico-olfactorius  septi. 

At  the  base  of  the  brain  the  temporal  and  occipital  lobes  cannot  be 
separated  from  one  another.  Longitudinally-directed  fissures,  in  smaller 
number,  traverse  the  region  common  to  both  lobes,  which,  in  general,  is 
included  in  the  temporal  lobe.  The  middle  temporal  gyrus  extends  only  a 
short  distance  toward  the  base;  that  which  is  visible  belongs  almost  en- 
tirely to  the  inferior,  or  third,  temporal  gyrus.  This  is  separated  by  means 
of  a  rather  superficial  fissure, — which  is  almost  always  interrupted  several 
times, — the  sukus  temporalis  inferior,  from  a  long,  spindle-shaped  convolu- 
tion, the  gyrus  fusiformis, — a  gyrus  invariably  well  defined.  This  gyrus 
borders  directly  on  the  long  gyrus  hippocampi.  It  is  separated  from  the 
hippocampal  gyrus  by  a  long,  deep  fissure,  a  fissure  appearing  very  early  in 
embryonic  life,  the  fissura  collateralis.  The  collateral  fissure  extends  over 
the  entire  under  surface  of  the  brain  from  the  occipital  lobe  to  the  apex  of 
the  temporal  lobe. 

The  fissures  of  the  brain  may  be  very  easily  fixed  in  mind  by  studying 
them  on  the  developing  brain  instead  of  on  that  of  the  adult.  At  the  same 
time,  several  facts,  very  interesting  from  a  morphological  stand-point,  are 
disclosed  as  an  additional  compensation. 

If  the  very  young  brain  is  examined,  which  is  shown  in  Fig.  20,  it  is 
seen  that  a  fissure  runs  along  the  greater  part  of  the  inner  edge  at  the  place 
where  the  wall  of  the  forebrain  passes  over  into  the  thin  velum  interpositum, 
which  consist  of  epithelium  only.  The  two  walls  of  the  fissure  are  formed 
just  by  this  epithelial  plate.  His  has  named  it  the  fissura  chorioidea.  Later 
in  life  it  is  filled  up  by  the  vessels  growing  into  it,  and  it  is  then  no  longer 
demonstrable,  because  its  walls  form  the  covering  of  the  plexus  chorioideus. 

Even  during  the  second  and  third  months,  a  second  fissure  is  met  with, 


202  ANATOMY   OF   THE    CENTRAL    NEEVOUS    SYSTEM. 

the  fissura  arcuata.  Somewhat  dorsal  to  the  fissura  chorioidea,  which  in- 
dicates, in  a  measure,  the  edge  of  the  hemisphere,  it  runs  in  a  curved  course 
on  the  inner  side  of  the  brain  around  this  edge,  thus  separating  the  funda- 
ment of  the  marginal  convolution,  or  gyrus  cinguli.  The  gyrus  fornicatus 
is  formed  later  from  the  frontal  portion  of  the  marginal  gyrus,  the  gyrus 


Fig.  135. — The  convolutions  on  the  base  of  the  brain  (schematic). 
The  chiasma  turned  back. 


hippocampi  from  its  caudal  portion.  It  will  be  remembered,  when  it  is 
here  learned  how  early  the  marginal  gyrus  is  differentiated  from  the  wall 
of  the  brain,  that  in  amphibians  and  reptiles  this  same  region  of  the  brain 
was  described  as  that  part  which  possesses  phylogenetically  the  oldest  cor- 
tical covering. 


THE    FORM-RELATIOXS    OF    THE    HUMAX    BEA1X.  203 

The  brain  that  we  are  considering  is  still  smooth  on  the  outer  surface  and  just 
slightly  differentiated  on  the  mesial  surface  by  the  fissura  arcuata.  Now,  however, 
about  the  beginning  of  the  third  month,  there  is  presented  a  beautiful  confirmation 
of  the  proposition,  previously  stated,  namely:  that  the  fissures  of  the  brain  result 
from  the  difference  in  growth  between  the  roof  of  the  skull  and  the  developing 
fundaments  within  the  brain.  Fissures  appear  only  in  Primates,  the  brains  of  which, 
.as  is  known,  attain  the  greatest  expansion,  which  fissures  are  arranged  in  the  form 
of  a  fan  on  the  inner  and  outer  side  of  the  brain.  They  converge  toward  the  base 
of  the  skull  and,  varying  in  number  and  formed  essentially  on  the  mesial  wall,  have 
exactly  the  direction  that  would  be  expected  and  required  if  the  brain  met  with 
compression  or  pressure  during  the  expansion  of  its  mantle. 

Some  time  during  the  course  of  the  fourth  month,  simultaneously  with  the  de- 
velopment of  the  fibers  of  the  corpus  callosum  between  the  hemispheres,  these  pri- 
mary fissures  disappear,  and  at  the  beginning  of  the  fifth  month  the  entire  hemisphere 
is  again  smooth.  These  transitory  fissures  have  never  been  found  in  other  mammals, 
but  I  may  communicate  to  you  the  interesting  fact  that,  under  certain  circumstances, 
in  cases  with  an  abnormal  rate  of  development,  fissures  having  a  similar  direction 


Fig.  136. — Transitory  fissures  of  the  brain.    Brains  of  fetuses  of  the  eleventh 
and  thirteenth  weeks.     (After  Cunningham.) 

•cover  the  surface  of  the  adult  brain.     Purely  mechanical  disturbances  lead  to  such 
radial  fissuring,  as  the  example  illustrated  by  Fig.  137  at  once  shows. 

In  several  of  the  lower  mammals  also,  as  in  the  Marsupials,  such  radially  placed 
fissures  are  here  and  there  found  on  the  brain. 

Although  the  transitory  fissures  have  commonly  disappeared  by  the 
fifth  month,  a  certain  tendency  to  the  development  of  similar  fissures  still 
remains.  The  fissura  parieto-occipitalis  develops  very  early  (see  Fig.  132) 
in  exactly  the  course  of  such  a  transitory  fissure  which  previously  had  a 
similar  direction;  and  on  the  outer  side  of  'the  brain  there  is  found — in 
apes,  at  least — a  continuation  probably  passing  out  from  it,  the  fissura  per- 
pendicularis  ext.  The  fissura  calcarina,  which  is  demonstrable  very  early, 
also  lies  in  the  direction  of  this  old  transitory  fissure. 

Now,  however,  probably  toward  the  end  of  the  fifth  month,  there  begins 
the  development  of  those  fissures  which  we  have  previously  become  familiar 


204 


ANATOMY   OF    THE    CENTRAL   NERVOUS    SYSTEM. 


with  from  the  study  of  the  adult  brain.  The  Sylvian  fossa,  the  origin  of 
which  was  earlier  explained,  becomes  narrower;  the  Avail  of  the  brain  around 
about  it  grows  and  soon  hangs  down  over  it  on  all  sides.-  The  insula  begins 
to  disappear  at  the  bottom  of  the  fissure;  the  edges  of  the  fossa  approach 
one  another  more  and  more,  and  finally  meet  toward  the  end  of  foetal  life. 


Fig.  137. — Large  scar  on  the  outer  side  of  a  cerebrum.     All  the  convolutions  con- 
verge toward  the  point  where  the  brain  could  not  expand.     (After  Ziegler.) 

The  fissura  Sylvii,  with  its  branches,  now  alone  affords  access  to  the  fossa 
over  the  insula  Eeilii,  which  was  at  one  time  wide  open. 

By  the  end  of  the  fifth  month  the  fundament  of  the  central  fissure  has- 
appeared  dorsal  to  the  fissure  of  Sylvius. 

Gradually,  in  the  course  of  the  sixth  and  seventh  months  all  the  other 


Fig.  138. — Brain  at  the  end  of  the  seventh  month. 

fissures  follow  the  few  fissures  just  mentioned.  But  they  are  still  so  little 
branched  and  so  simply  arranged  that  a  glance  at  a  fetal  brain  at  the  end 
of  the  seventh  month  is  sufficient  in  order  to  survey  at  once  the  most  im- 
portant parts  of  the  fissuration  of  the  brain  (Fig.  138). 

That  which  here  lies  before  us  resembles  a  schema  of  the  fissures  of  the 


THE    FOBM-RELATIONS    OF   THE    HUMAN    BKAIX.  205 

adult  brain.  The  central  convolutions  in  front  and  behind  the  central 
fissure;  the  three  frontal  gyri,  still  incompletely  separated  from  one  an- 
other; the  superior  and  inferior  parts  of  the  parietal  lobe,  between  which 
the  three  components  of  the  fissura  interparietalis  are  visible;  finally  the 
temporal  lobe  divided  into  three  parts — these  are  all  prominent,  and,  when 
once  understood,  make  their  recognition  later  in  the  adult  brain  a  very 
easy  matter. 

The  great  interest  which  is  shown  in  the  development  and  perfection  of  the 
brain-fissures  is  not  occasioned  purely  by  morphology.  Since  the  scientific  study  of 
the  brain  has  become  general,  there  has  been  an  endeavor  to  answer  the  question, 
whether  the  intellectual  status  of  the  individual  may  somehow  be  reflected  in  the 
expansion  of  the  surface  of  the  cerebrum.  Gall  even  believed  himself  justified  in 
laying  down  the  proposition  that  men  ranking  especially  high  intellectually  have 
larger  and  more  richly  convoluted  cerebrums  than  others,  and  that  the  frontal  lobes 
are  preponderantly  better  developed. 

Here,  however,  we  are  dealing  with  a  general  impression  rather  than  with  the 
result  of  exact  measurement  and  comparative  observation.  Really  serious  studies  in 
this  direction  first  date  from  the  time  when  Rudolph  Wagner,  in  1860,  presented  to 
the  Gottingen  Society  of  Sciences  the  report  of  the  investigations  which  he  had  made 
on  the  brain  of  the  celebrated  mathematician,  Gauss,  and  on  several  other  brains  of 
philosophers  and  men  of  letters.  Since  then  we  have  come  into  possession  of  a  very 
large  number  of  descriptions  of  convolutions. 

There  is  hardly  a  fissure,  hardly  a  convolution,  that  cannot  now  present  a  small 
literature  of  its  own.  The  typical  relations  as  regards  the  direction  and  a  certain 
number  of  possible  variations  are  well  known  for  all  the  sulci  and  gyri.  We  possess 
descriptions  of  the  surface  of  the  brain,  not  only  of  Europeans,  but  also  of  repre- 
sentatives of  many  foreign  peoples.  The  anthropoid  apes  have  been  made  the  sub- 
ject of  very  numerous  investigations,  and  a  very  zealous  study  has  been  devoted  to 
the  other  apes  by  many  investigators.  The  development  of  the  convolutions  is  now 
exactly  known  for  man,  and  many  apes  also.  It  has  become  apparent  from  these 
studies  (Cunningham)  that  the  embryonic  fissures  and  convolutions  appear  by  no 
means  simultaneously  in  all  individuals,  nor  have  the  same  configuration  when  they 
are  once  distinctly  present.  This  fact  is,  therefore,  very  important,  because  it  con- 
tains the  proof  that  the  cortex  of  the  brain,  the  organ  of  the  higher  intellecttial 
activity,  is  variously  expanded  in  different  individuals,  even  in  the  fundament. 

If  no  mention  at  all  were  made  of  all  these  numerous  investigations  while  de- 
scribing the  convolutions  of  the  adult  human  brain,  investigations  that  have  made 
us  familiar  with  the  variations  to  which  the  individual  gyri  are  subject,  it  was 
because  these  things  are,  for  the  present,  only  to  be  recorded  and  as  yet  are  to 
be  brought  into  no  sort  of  connection  with  the  perfection  of  the  separate  intellectual 
faculties.  For  investigations  of  the  brain  are  still  wanting  entirely  which  consider, 
simultaneously  with  the  development  of  the  gyri,  the  entire  intellectual  status  of  a 
single  individual.  Even  now,  when  numerous  careful  researches  have  finally  fur- 
nished us  somewhat  of  a  survey,  we  are  still  hardly  able  to  consider  such  relations. 
However,  the  attempt  must  be  made  even  now  to  investigate  the  corresponding  cor- 
tical development  for  the  faculties  known  to  be  localized.  It  is  hoped  the  time  will 
then  come  when  the  convolutions  will  be  no  longer  described  simply  as  such,  but 
only  in  connection  with  the  questions  which  their  development  always  gives  rise  to  in 


206  ANATOMY    OF    THE    CENTRAL   NERVOUS    SYSTEM. 

individual  cases.  Absolutely  nothing  is  known  of  the  possessors  of  almost  all  of  the 
brains  previously  described.  Thus  a  very  large  part  of  the  data  collected  seems  to 
me  next  to  worthless,  and  later  will  probably  be  entirely  so,  for  the  point  in  ques- 
tion from  which  we  proceeded,  the  discovery  of  relations  between  the  configuration 
of  the  brain  and  the  intellectual  status  of  the  possessor. 

Now  the  attempt  has,  indeed,  been  made  to  decide  the  question  whether  greater 
intelligence  may  correspond  to  a  larger  brain,  by  weighing.  Thousands  and  thousands 
of  such  estimates  have  been  made,  but  the  large  amount  of  material  thus  obtained 
contains  little  that  is  of  any  value.  First  of  all,  the  body-weight  has,  in  many  cases, 
not  even  been  considered.  This,  however,  increases  according  to  factors  quite  dif- 
ferent from  those  controlling  the  brain;  nevertheless,  a  certain  connection  exists 
between  the  size  of  the  two.  Then,  however, — and  this  appears  to  me  the  most  im- 
portant,— the  development  of  the  cerebrum  as  a  whole  cannot  be  used  at  all  as  a 
measure  of  the  sum  total  of  intelligence.  It  is  an  acquisition  of  the  last  decade  only, 
that  we  have  learned  that  different  brains  may  have  a  very  different  development 
of  their  various  regions.  At  present  these  cortical  regions  cannot  be  so  separated 
from  one  another  that  they  may  be  compared  morphologically  or  by  weight.  The 
brain-weight  for  the  majority  of  males  ranges  between  1300  and  1450  grammes;  for 
females  it  is  a  little  less.  Now,  uncommonly  heavy  brains  occur  at  times  in  indi- 
viduals who  do  not  rank  very  high  intellectually,  and,  on  the  other  hand,  relatively 
low  weights  have  been  found  in  men  of  prominence.  We  are  not  accustomed,  how- 
ever, to  measure  a  man's  intellectual  value  in  its  entirety,  which,  indeed,  is  almost 
never  possible,  but  generally  according  to  some  especially  prominent  characteristic, 
which  gives  authority,  position,  etc.,  to  the  individual.  Such  peculiarities  may  very 
well  be  traced  to  the  increased  development  of  a  single  cortical  region,  this  increase 
not  directly  expressing  itself  in  the  general  relations  of  the  gyri  or  in  the  brain- 
weight.  Anyone  endowed  wTith  enormous  visual  memory,  visual  imagery,  etc.,  and 
with  all  the  intellectual  attributes  that  characterize  the  great  artist,  might  occupy 
a  position  entirely  unique,  yet  the  increased  development  of  the  occipital  lobe  would, 
on  weighing,  show  no  essential  variation  from  the  average  brain-weight  if,  perhaps, 
other  centres  were  developed  to  a  less  degree.  The  same  may  be  said  of  a  musician, 
where,  in  all  probability,  we  have  to  do  with  an  increase  of  the  temporal  lobe. 

One  who  is  a  great  orator,  an  energetic  man,  and  an  ingenious  commander  need 
not  necessarily  possess  a  larger  brain.  These  characteristics  may  well  be  based  upon 
very  small  local  increases  of  single  cortical  areas.  Gambetta's  brain,  for  example,  the 
speech-area  of  wThich  was  described  as  uncommonly  developed  (see  above),  weighed 
hardly  more  than  the  average  of  the  smaller  brains.  At  present  so  little  is  known 
regarding  the  cortical  areas  that  in  general  hardly  more  can  be  said  than  that  espe- 
cial development  of  the  frontal  lobes  frequently  goes  hand  in  hand  with  high  in- 
tellectual qualities,  and  that  insufficient  endowment,  even  idiocy,  is  found  to  be 
comparatively  frequent  in  those  with  abnormally  small  frontal  lobes.  That  which 
is  still  entirely  wanting  and  is  not  to  be  attained  at  all  at  the  present  time,  is  data 
of  weight  for  the  separate  regions  of  the  cortex.  From  this  state  of  affairs  it  will 
be  understood  why  I  do  not,  at  the  present  time,  give  anything  more  definite  con- 
cerning the  weight-relations  of  the  central  nervous  system. 

It  first  occurred  to  Perls,  my  late  friend,  that  a  comparatively  large  number 
of  men  who  are  intellectually  eminent  give  the  impression  from  their  type  of  face 
that  they  may  have  had  an  hydrocephalus,  which  healed  in  early  childhood.  He 
expressed  the  conjecture  that,  if  a  moderate  hydrocephalus  should  recede,  a  resist- 
ance which  is  proportionally  much  less  would  oppose  the  growth  of  the  brain,  on 
account  of  the  enlarged  skull.  Since  then  I  have  followed  this  suggestion  which  he 


THE    FORM-RELATIONS    OF    THE    HUMAN    BRAIN.  207 

gave  me,  and  have  found  proofs  of  its  correctness  in  not  a  very  small  number  of 
cases.  Rubinstein's  powerful  skull,  for  example,  showed  on  section,  according  to 
newspaper  accounts,  very  clear  evidences  of  an  old  rachitis;  and  we  even  know 
that  Cuvier,  who  had  an  uncommonly  heavy  brain,  was  hydrocephalic  in  child- 
hood. Whoever  carefully  examines  a  good  collection  of  photographs,  following  the 
suggestion  given  by  Perls,  will  meet  with  many  faces  that  are  manifestly  of  an 
hydrocephalic  nature,  and  precisely  in  men  who  rank  especially  high  intellectually. 
Naturally,  all  men  of  high  intellectual  attainment  are  not  healed  hydrocephalics,  any 
more  than  every  healed  hydrocephalic  must  have  a  better  development  of  the  brain 
as  a  consequence. 


CHAPTER    XIV. 
THE   BRAIX   OF   MAMMALS   AXD   THE   OLFACTORY   APPARATUS. 

IN  the  first  chapters  the  relations  of  the  forebrain  of  mammals  could 
only  be  touched  upon  in  a  very  general  way.  At  present,  when  you  are 
better  acquainted  with  the  structure  of  the  human  brain,  it  will  pay  you  to 
glance  at  other  mammalian  brains.  Much  of  that  which  is  known  regarding 
the  fiber-systems,  etc.,  has  been  gained,  as  you  know,  not  from  the  human 
brain,  but  from  a  study  of  that  of  animals.  A  great  many  things  that  appear 
hardly  intelligible  in  human  brains  are  met  with  much  better  developed  in 
lower  vertebrates. 

If  it  is  desired  clearly  to  understand  the  enormous  differences  in  degree 
of  perfection  of  the  mantle  of  the  forebrain  which  are  found  in  the  various 
mammals,  they  must  be  considered  in  regard  to  a  fact  which  up  to  the 
present  time  has  not  been  sufficiently  recognized.  The  mantle  is  not  a  unit 
functionally.  It  is  composed  rather  of  a  large  number  of  different  parts — 
called  centers — and  numerous  physiological  experiments  have  shown  that 
movements  which  must  be  acquired,  and  probably  most  of  the  intellectual 
combinations,  are  only  made  possible  by  the  existence  of  such  centers. 

The  introductory  chapters  have  shown  that  the  real  motor  and  sensory 
centers  are  situated  low  down,  from  the  spinal  cord  to  the  midbrain,  and 
that  these,  even  if  the  forebrain  is  wanting,  are  in  themselves  sufficient 
for  necessary  activity.  These  centers,  present  in  abundance  and  found  at 
an  early  period,  are  connected  with  one  another  to  form  series. 

Experimental  physiology  shows,  however,  that  many  of  the  lower  centers  are 
connected  with  higher  centers,  located  above  in  the  cortex,  in  such  a  manner  that 
irritation  of  the  latter  produces  movement.  Of  what  nature  and  importance  the  in- 
fluence of  the  higher  centers  on  the  lower  may  be  is  still  a  matter  of  special  dis- 
cussion. For  this  reason  an  endeavor  has  been  made  to  study  as  exactly  as  possible 
the  phenomena  that  appear  after  the  removal  of  portions  of  the  cortex.  Doubtless 
the  importance  of  the  role  played  by  the  cerebral  cortex  is  different  in  different  verte- 
brates. While  the  removal  of  the  entire  cerebrum  in  lower  vertebrates  does  not  de- 
stroy the  ability  to  perform  coarser  movements  with  efficiency,  in  mammals,  after  de- 
struction of  circumscribed  portions  of  the  motor  zone,  paralyses  appear,  which  are 
very  transitory.  In  man  disease  even  of  relatively  small  portions  of  the  cortex  often 
leads  to  permanent  paralyses.  Manifestly  all  motor,  and  many  senso-psychical,  func- 
tions may  'be  performed  by  parts  of  the  central  nervous  system  situated  lower  dotcn. 
The  higher  toe  ascend  in  the  vertebrate  series,  however,  the  more  is  the  cortex  con- 
cerned in  the  activity  of  the  brain,  and  the  more  is  consciousness  met  with  as  a  con- 

(208) 


THE    BRAIX    OF    MAMMALS   AXD    THE    OLFACTORY   APPARATUS.          209 

comitant.  Man  has.  in  this  respect,  reached  a  stage  where  many  of  the  functions  con- 
cerned can  no  longer  be  executed  without  the  participation  of  the  cortex.  All  the 
possible  transition-stages  are  observed  in  mammals.  It  is  true  that  the  separate 
muscles,  etc.,  can  be  influenced  in  mammals  through  irritation  of  the  cortex,  but  the 
parts  of  the  cortex  thus  involved  are  not  necessary  for  the  movements  concerned. 
In  man,  however,  the  greater  portion  of  the  surface  of  the  forebrain  has  become  in- 
dispensable. 

Morphologically,  this  relation  expresses  itself  in  a  very  different  develop- 
ment of  the  various  parts  of  the  brain-mantle.  At  present  the  essential  parts 
of  the  mantle  can  be  distinguished  from  one  another  in  a  few  mammals  only; 
yet  it  is  already  known  that  the  development  of  the  cortex  is  continuous  in  the 
mammalian  series.  There  exists  the  greatest  of  variations  and  the  most 
variable  of  size-relations;  yet  even  at  present  the  position  which  a  few  of 
the  mammals  occupy  in  the  entire  series  can  be  indicated.  Even  a  super- 
ficial consideration  of  mammalian  brains  shows  that  one  center  especially, 
the  olfactory  center,  presents  most  varying  size-relations,  so  considerable, 


Fig.  139. — Brain  of  an  armadillo:     Dasypus  villosus.     (Side-view.) 
The  olfactory  apparatus  is  shaded. 

sometimes,  that  the  entire  remaining  portion  of  the  mantle  appears  to  be  a 
small  appendage  only  of  the  olfactory  lobe. 

The  olfactory  brain  is  that  part  of  the  cortex  which  first  appears  in  the 
animal  series;  the  other  cortical  regions  become  only  later  associated  with 
this.  Among  many  of  the  lower  mammals  animals  are  known  which  possess 
rudiments,  at  first  only  relatively  small,  of  that  portion  of  the  mantle  which 
does  not  belong  to  the  olfactory  apparatus.  In  such  a  case,  the  olfactory 
lobe,  and  whatever  else  belongs  to  the  cortical  olfactory  apparatus,  often 
forms  almost  one-half  of  the  entire  mass  of  the  forebrain. 

What  is  known  regarding  the  manner  of  life  of  such  "olfactory"  animals  agrees 
well  with  the  structure  of  their  brains.  The  small  armadillo,  for  example,  the  brain 
of  which  is  represented  above,  spends  its  entire  life  burrowing  in  the  soil  and  creep- 
ing about  under  the  foliage  of  the  dense  primeval  forests.  For  choosing  its  food,  for 
finding  it,  no  sensory  apparatus  will  be  so  important  to  it  as  that  of  smell.  The 
uniformly  limited  activities  of  the  plump  body  will  need  fewer  acquired  and  de- 
liberate acts  than  the  prehensile  hand  of  an  ape,  perhaps.  In  the  latter,  therefore, 
we  should  expect  a  much  greated  development  of  the  true  psychical  centers  for  the 
upper  extremities  than  in  the  small  creature  that  lives  by  wallowing.  This,  in  fact, 


230  ANATOMY   OF    THE    CEXTEAL    XEEVOUS    SYSTEM. 

is  what  occurs.  At  present,  moreover,  we  can  even  occasionally  conclude  from  the 
development  of  a  definite  cortical  region  the  existence  of  an  ability  to  execute  in 
a  certain  direction.  The  elephant,  for  example,  possesses  an  especially  large  cortical 
field  in  the  region  of  the  cortex  where  the  facial  area  is  localized  in  the  higher 
mammals.  This  is  entirely  wanting  in  the  rhinoceros  and  tapir.  If  nothing  were 
known  of  the  wonderful  ability  of  the  animal  to  use  its  trunk  in  such  various  ways, 
it  might,  however,  be  conjectured  from  the  presence  of  the  above-mentioned  field  in 
the  facial  area  that  from  this  center  muscles  were  innervated  which  were  capable  of 
very  special  function. 

All  the  investigations  on  the  mantle  lead  to  the  conclusion  that  it  is 
composed  of  separate  areas,  which  may  vary  in  relative  size.  One  part  of 
these  centers  stands  in  relation  to  motor  and  sensory  processes.  Another 
part,  as  yet  studied  in  man  only,  contains,  according  to  the  brilliant  dis- 
covery of  Flechsig,  association-regions  alone  which  are  well  adapted  struct- 
urally to  form  connections  with  one  another  and  with  other  centers.  Ac- 
cording to  Flechsig,  it  is  probable  that  the  intellectual  superiority  of  the 
Primates  rests  upon  the  high  degree  of  perfection  of  the  "centers  of  asso- 
ciation." In  point  of  fact,  the  brain-mantle  generally  increases  in  such  a 
manner  that  a  larger  mantle  is  found  in  the  more  intelligent  animals  than 
in  those  especially  deficient  mentally  and  of  low  rank.  It  will  be  the  object 
of  continued  investigation  to  show  how  the  individual  elements  grow.  The 
interest  which  investigations  in  the  comparative  anatomy  of  the  cerebral 
convolutions  really  have  lies  just  in  this  inquiry,  rather  than  in  purely  mor- 
phological considerations. 

Very  gradually,  then,  the  mantle  increases  in  extent  ascending  in  the 
vertebrate  series.  In  the  apes,  belonging  to  the  class  of  primates,  it  has 
attained  an  expansion  which  borders  closely  on  the  relations  found  in  man. 
Nevertheless,  an  important  factor,  besides  more  unessential  relations,  still 
separates  it  from  the  stage  reached  by  man.  The  frontal  lobe,  still  very 
small  in  the  lower  apes,  attains  a  large  size  in  the  higher  apes,  but  always 
remains  very  much  inferior  to  that  of  man.  In  man,  even,  this  develop- 
mental process  is  in  nowise  terminated  as  yet.  Differences  still  plainly 
occur  in  the  region  of  the  frontal  lobe  which  allow  us  to  infer  the  possi- 
bility of  further  perfecting.  The  inferior  region  of  the  frontal  lobe,  which 
contains  the  centers  of  speech,  and  shows  very  marked  variations  in  develop- 
ment, is  the  part  more  particularly  concerned. 

When  a  small  mantle  is  present  the  fibers  issuing  from  it  can  naturally 
be  only  few  in  number.  In  fact,  the  radiation  from  the  cortex  is  so  meagre 
in  many  smaller  mammals  that  a  real  centrum  semiovale  is  not  formed  at 
all — the  entire  fiber-system  more  frequently  being  limited  to  a  relatively 
thin  covering  under  the  cortex.  This  layer  of  white  matter  then  borders 
directly  upon  the  ventricle,  and  is  traversed  by  the  terminal  filaments  of 
its  epithelium. 


THE   BRAIX    OF    MAMMALS    AXD   THE    OLFACTORY   APPARATUS.          211 

Moreover,  the  principal  commissure  of  that  portion  of  the  mantle  which 
does  not  belong  to  the  olfactory  apparatus,  the  corpus  callosum,  is  also  so 
small  that  it  occupies  a  relatively  small  portion  only  of  the  mesial  surface 
of  the  hemisphere.  Indeed.,  in  some  monotremes  and  in  the  marsupials 
hitherto  investigated  a  corpus  callosum  is  entirely  wanting  (Symington,  E. 
Smith). 

Likewise,  the  fiber-systems  passing  down  from  the  mantle,  especially 
those  to  the  pons  and  the  spinal  cord,  the  fibers  of  the  pes,  are,  in  all  verte- 
brates very  much  less  developed  than  in  man. 

For  the  most  part  the  olfactory  apparatus  is  much  more  powerfully 
developed  than  in  man,  but  it  may  also  atrophy  very  enormously,  even 
degenerate  to  such  an  extent  that  it  almost  disappears,  as  in  the  aquatic 
mammals.  Accordingly,  mammals  have  been  divided  into  osmatic  and 


Fig.  140. — Brain  of  armadillo:    Dasypus  villosus.     (Basal  view.) 

anosmatic.  The  investigation  of  a  very  large  series  of  animal  brains  shows 
that  the  olfactory  apparatus  and  the  pallium  develop  entirely  independently 
of  one  another  phylogenetically ;  that  the  one  may  atrophy,  the  other  attain 
a  higher  degree  of  perfection;  and  vice  versa.  The  greater  perfection  of  the 
olfactory  apparatus  manifests  itself  not  only  in  the  more  powerful  develop- 
ment of  the  olfactory  lobe  and  the  olfactory  region  of  the  mantle,  but  also, 
on  the  other  hand,  in  a  very  marked  development  of  definite  cell-groups  and 
fibers  belonging  to  this  apparatus  in  other  parts  of  the  brain. 

The  olfactory  apparatus  will,  therefore,  be  considered,  first  of  all,  as  a 
whole.  Present  in  man,  as  relatively  atrophied  remnants  only,  it  may  be 
more  easily  studied  in  many  other  mammals. 

Illustrations  are  here  presented  of  the  base  of  the  brain  of  a  calf  and 
of  an  armadillo.  A  large  lobe  is  here  seen  which  anteriorly  is  covered  as  if 
with  a  cap  by  an  enlargement,  and  posteriorly  passes  over  somewhat  directly 


212 


AXATOMY    OF   THE    CENTRAL    XERYOUS    SYSTEM. 


into  the  convolution  of  the  cormi  Ammonis.  This  is  the  olfactory  brain. 
In  the  armadillo — and  in  the  dog,  rabbit,  and  many  other  mammals  also — 
it  is  much  larger  than  in  the  calf.  It  then  nearly  always  occupies  the  entire 
base  of  the  brain.  This  is  the  same  part  of  the  brain  which,  in  reptiles,  first 
made  its  appearance  as  a  separate  region  of  the  mantle.  See  Chapter  XII, 
pages  170  and  171. 

The  fila  olfactoria,  cut  off  unevenly  in  the  specimen,  enter  the  anterior 


Fig.  141. — The  base  of  a  calf's  brain.  The  ventricle  purposely  opened  from 
below  in  order  to  show  its  recesses:  the  R.  opticus,  infundibuli,  and  mamillaris. 
Riechbundel,  olfactory  bundle. 


part.  The  bulbus  olfadorius  is  shortly  met  with.  This  rests  upon  the  lobus 
olfactorius  anterior,  the  frontal  division  of  the  entire  apparatus.  The  lobus 
olfactorius  anterior  then  passes  over  into  the  lobus  olfactorius  posterior, 
which  is  particularly  well  defined  in  the  armadillo  (Dasypus).  In  Fig.  141 


THE    BRAIX    OF    MAMMALS   AND    THE    OLFACTOEY   APPARATUS.          213 

it  is  designated  as  the  spatium  olfactorium  (olfactory  area,  or  espace  quadri- 
latere  of  Broca). 

To  this  entire  apparatus  there  is  added  posteriorly  the  cortical  area,  or 
field,  of  the  olfactory  apparatus,  which  has  been  designated,  on  account  of  its 
shape,  as  the  lobus  pyriformis.  Mesially,  this  pyriform  lobe  passes  directly 
over  into  the  territory  of  the  gyrus  hippocampi. 

The  long  fissura  limbica  separates  the  olfactory  brain  from  the  remain- 
ing pallium. 

The  fibers  of  the  olfactory  nerve  dip  into  the  bulbus.  A  section  through 
the  bulbus  reveals  a  distinct  separation  of  the  tissues  into  layers.  As  would 
be  expected,  the  fibers  of  the  olfactory  nerve  lie  most  externally.  Then 
follows  a  grayish-white  zone,  in  which,  even  with  the  naked  eye,  there  are 
visible  numerous  small  balls,  the  glomeruli  olfactorii;  it  is  known  as  the 
layer  of  the  glomeruli.  Within  this  lies  the  gray  layer  of  ganglionic  cells, 
which  then  gradually  passes,  by  means  of  a  "granular  zone,"  over  into  the 
olfactory  medulla.  A  delicate  extension  of  the  lateral  ventricle  reaches 
into  the  bulbus.  The  ventricular  epithelium  borders  immediately  upon  the 
layer  of  medullated  fibers. 

Investigations  by  Golgi,  S.  and  P.  Ramon  y  Cajal,  and  those  by 
Gehuchten  and  Kolliker  have  made  us  familiar  with  the  elements  of  these 
layers,  and  with  the  very  interesting  connection  of  some  of  these  elements 
with  the  fibers  of  the  olfactory  nerve. 

The  fibers  of  the  olfactory  nerve  are  no  other  than  the  centrally  directed  ter- 
minal processes  of  the  sense-cells  of  the  olfactory  mucous  membrane.  This  fact  has 
already  been  referred  to  while  describing  the  embryology. 

After  these  fibers  have  passed  the  cribriform  plate  of  the  ethmoid  and  arrived 
at  the  ventral  surface  of  the  bulbus,  they  undergo  repeated  decussations,  and  then 
sink  into  the  substance  of  the  brain.  There  each  neuraxon  immediately  breaks  up 
into  a  delicate  terminal  arborization.  The  arborization  meets  with  the  thick  branches 
of  a  dendritic  process,  which  is  similarly  branched,  and  both  varieties  of  fibers,  which 
lie  in  immediate  contact  with  one  another,  together  form  a  roundish  complex:  the 
glomerulus  olfactorius. 

The  dendritic  process  arises  from  a  ganglionic  cell,  which  gives  off  similar  proc- 
esses in  abundance.  Only  one  of  them  constantly  enters  into  the  described  relation 
with  the  olfactory  nerve-fibers.  Each  of  these  cells  of  the  brain  is  connected  with 
quite  a  number  of  olfactory  fibers.  Such  cells,  varying  in  form  and  size,  lie  in  large 
numbers  in  the  gray  layer  under  the  glomeruli.  Each  sends  its  neuraxon  centrally; 
it  may  be  followed  as  far  as  the  layer  of  medullated  fibers.  At  times  it  gives  off 
collaterals  on  the  way.  Here  is  a  good  example  of  what  was  spoken  of  in  the  chapter 
on  the  combination  of  the  tissues  of  the  central  organs.  The  primary  and  the  sec- 
ondary olfactory  pathways  are  seen  directly  before  you,  and  it  is  recognized  that 
the  connection  is  brought  about  through  the  splitting-up  of  the  neuraxon  of  the 
primary  pathway  and  its  contact  with  the  dendritic  processes  from  the  secondary. 

A  number  of  other  elements  (the  nervous  nature  of  which  is  still  in  doubt) 
were  also  found  in  the  cortex  of  the  alfactory  bulb.  Between  the  cells  mentioned  and 


214: 


ANATOMY    OF    THE    CENTEAL    NEBVOUS    SYSTEM. 


the  layer  of  medullated  fibers,  partly  within  the  same  also,  lie  the  cells  hitherto 
designated  as  "granules."  I  have  shown  three  types  of  these  in  the  accompanying 
illustration  (a,  b,  c).  Moreover,  cells  with  a  very  much  branched  neuraxon  are  every- 
where present  (e). 

The  fibrous  net-work,  which  all  these  elements  form,  is  naturally  made  much 
more  complicated  on  account  of  the  fact  that  the  neuroglia-cells  lie  everywhere 
within  it,  and  that  the  processes  of  the  ventricular  epithelium  extend  far  into 
the  substance  of  the  bulbus  olfactorius.  The  illustration,  combined,  in  the  main, 


Medulla  of  the  lotms 


Mitral  cells  of  the  cortex 


Surface  of  the  cortex  with  the  glom-; 
eruli  and  the  fila  olfactoria  / 


Fig.  142. — Section  through  the  olfactory  mucous  membrane,  the  lamina 
cribrosa,  and  the  bulbus  olfactorius.  The  elements  are  combined  schematically, 
but  the  relations,  especially  the  branching  and  form,  are  taken  from  preparations. 


from  drawings  by  Van  Gehuchten,  was  kept  as  simple  and  diagrammatic  as  possible. 
Everything  must  be  imagined  much  denser  and  richer  in  fibers  and  cells. 

The  entire  formation  of  the  bulbus  may  be  easily  traced  back  to  the 
common  cortical  type.  If  Fig.  142  is  turned  upside  down  and  compared  with 
Fig.  152,  that  fact  is  apparent  at  once.  The  text  to  the  left  of  Fig.  142  is 


THE    BRAIN    OF    MAMMALS    AXD    THE    OLFACTORY    APPARATUS.          215 

intended  to  simplify  the  comparison.    The  entire  formation  of  the  bulbus  is 
there  designated  as  the  cortex  of  the  lobus. 

The  gray  mass  of  the  bulbus  sends  backward  the  central  secondary  and 
tertiary  pathways  of  the  olfactory  apparatus.  First  of  all,  such  a  pathway 
extends  constantly  to  the  surface  of  the  lobus,  where,  now  splitting  up  into 
several,  now  into  fewer,  strands,  it  passes  backward.  In  so  doing  small 
fibers  continually  pass  down  from  this  lateral  olfactory  radiation  deep  into 
the  cortex  of  the  lobus.  Yet  the  tract  is  not  exhausted  by  this;  on  the  con- 
trary, its  fibers,  passing  over  the  olfactory  area,  extend  farther  backward 
until  in  the  region  of  the  nucleus  amygdalae.  All  of  these  fibers  have  a 
large  diameter,  and  have  been  known  for  a  long  time  as  the  roots  of  the 
olfactory  nerve. 

In  the  description  of  the  lower  vertebrate  brain  they  have  been  more  closely 
followed,  and  we  have  been  able  to  confirm  the  fact  that  a  part  certainly  passes 
into  the  cortex  of  the  olfactory  lobe,  just  as  in  the  mammals  above,  and  that,  in 
addition  to  these  tractus  bulbo-corticales,  a  tract  of  fibers  is  present,  which,  running 
in  a  similar  course,  soon  separates  and  ends  in  the  epistriatum.  This  epistriatum  has 
not  yet  been  found  in  mammals,  because  only  now  are  we  in  a  position  to  seek  for 
it,  seeing  that  its  existence  has  been  recognized  so  distinctly  in  lower  brains.  Never- 
theless, it  is  very  probable  that  good  guides  to  that  still-undiscovered  portion  of  the 
brain  are  possessed  in  those  tracts  of  fibers  that  extend  into  the  more  posterior  re- 
gion: into  the  lobus  pyriformis  and  into  the  neighborhood  of  the  nucleus  amygdalae. 

From  the  olfactory  radiations  from  the  bulbus  there  must  be  dis- 
tinguished a  tract  which  hitherto  has  been  regarded  as  part  of  it,  and  called 
the  mesial  root  of  the  olfactory  nerve.  There  develop,  namely,  from  the 
medulla  of  the  bulbus,  numerous  finer  nerve-fibers,  which  pass  away  beneath 
the  cortex  into  the  medulla  of  the  lobus.  In  it  they  mix  with  the  medullated 
fibers  of  the  lobus  in  such  a  manner  that  they  are  not  separable  at  present. 
At  the  posterior  end  of  the,lobus,  directly  in  front  of  the  olfactory  field, 
however,  a  tract,  which  lies  in  its  continuation,  leaves  the  lobus  and  passes 
beneath  the  thin  cortex  of  the  olfactory  lobe  upon  the  inner  surface  of  the 
brain.  The  cortex  is  raised  up  somewhat  by  this  tract.  This  mesial  olfactory 
radiation,  passing  on  the  inner  side  of  the  brain  to  the  septum  pellucidum, 
extends  over  this  into  the  fornix,  and  from  there  into  the  cornu  Ammonis. 
It  is  always  less  white  than  the  lateral  radiation,  on  account  of  the  thin  cor- 
tical covering. 

A  fissure  separates  the  lobus  olfactorius  posterior  from  the  lobus  hippo- 
campi. This  structure,  always  uncommonly  large  in  the  osmatic  animals, 
contains  the  inrolling  of  the  cornu  Ammonis  at  its  mesial  edge.  It  is  hardly 
to  be  compared  with  the  small,  relatively  atrophied  convolution  of  the  cornu 
Ammonis,  the  gyrus  hippocampi,  in  man.  At  the  base  of  the  brain  the 
gyrus  hippocampi  follows  the  entire  edge  of  the  hemisphere,  passes  up  pos- 


216  ANATOMY    OF    THE    CENTRAL    NERVOUS    SYSTEM. 

teriorly  on  to  the  mesial  surface  of  the  brain,  and  here  runs  forward  some 
distance.  Its  subiculum,  the  cortex,  which  is  not  inrolled  and  lies  directly 
on  the  base  of  the  brain,  then  passes  immediately  over  into  the  lobus  supra- 
callosus — gyrus  fornicatus  in  man. 

In  man  the  hippocampal  gyrus  does  not  extend  up  under  the  corpus  callosum. 

Since  the  lobus  supracallosus  turns  down  anteriorly  to  the  base  of  the 
brain  and  appears  to  reach  again  the  olfactory  area  with  its  most  anterior 
end,  this  entire  portion  of  the  cortex  forms  a  kind  of  arch  around  the  margin 
of  the  hemisphere.  Broca,  who  first  discovered  that  the  various  cortical 
tracts  entering  it  all  stand  in  a  direct  relation  as  to  size  with  the  develop- 
ment of  the  olfactory  apparatus,  has  designated  the  lobus  limbicus — as  he 
named  the  entire  area — as  the  olfactory  cortex. 

It  is  a  question  with  me  whether  the  gyrus  fornicatus  belongs  to  the  olfactory 
apparatus. 

The  lobus  limbicus  is  always  separated  from  the  rest  of  the  brain  by  a 
large,  distinct  fissure:  the  fissura  limbica.  Its  upper,  curved  portion  has 
already  been  met  with  in  man  as  the  sulcus  cinguli.  According  to  the  in- 
vestigations of  Zuckerkandl,  the  gyrus  dentatus  and  its  continuation  upon 
the  upper  surface  of  the  corpus  callosum,  the  stria  of  Lancisi,  must  also  be 
included  in  the  lobus  limbicus.  All  of  these  gyri  which  thus  surround  the 
edge  of  the  hemisphere— the  lobus  olfactorius,  the  gyrus  hippocampi,  and 
the  gyrus  fornicatus,  the  stria  of  Lancisi  and  the  fascia  dentata — are  very 
strongly  developed  in  animals  having  highly  perfected  olfactory  organs. 
They  are  somewhat  atrophied  in  those  animals  which  have  small  olfactory 
lobes,  as  is  the  case  with  man.  In  the  dolphin,  which  has  no  olfactory  lobe, 
they  are  developed  the  least  of  all  (Broca,  ZuckerkandT).  These  parts  of  the 
brain,  belonging  manifestly  to  the  olfactory  apparatus,  are  included  with 
the  lobus  olfactorius  under  the  term  rhinenceplialon,  suggested  by  Turner. 
The  elements  of  the  rhinencephalon,  the  sulci  and  gyri,  may  be  demon- 
strated in  all  mammals  with  a  certain  constancy  of  arrangement. 

The  separate  parts  of  the  lobus  limbicus  of  the  right  and  left  side  are 
connected  with  one  another  by  a  large  commissural  system:  the  commissura 
anterior.  Its  anterior  pedicle  arises  in  the  lobus  olfactorius  of  the  one  side, 
and,  curved  in  the  shape  of  a  horseshoe,  passes  over  at  the  base  of  the  brain 
to  the  lobus  of  the  other  side.  A  posterior  pedicle  unites  the  lobi  cornuum 
Ammonis,  or  at  least  the  regions  of  the  cortex  which  lie  directly  without  the 
in-rolling  of  the  cornu  Ammonis.  Finally,  an  ascending  branch  of  the  an- 
terior commissure  is  recognized  in  many  mammals.  It  passes  into  the 
capsula  externa  and  is  well  adapted  to  connect  the  dorsal  part  of  the  mar- 
ginal gyrus  with  parts  lying  opposite. 


THE    BRAIX    OF    MAMMALS    AXD    THE    OLFACTOEY   APPARATUS.          217 

The  cornua  Ammonis  themselves  possess  a  distinct  communication  with 
one  another:  an  extensive  system  of  fibers  extends  between  them.  It  is 
called  the  commissure  of  the  cornu  Ammonis,  or  the  psalterium. 

The  cornu  Ammonis  is  connected  with  the  olfactory  lobe  by  the  mesial 
olfactory  radiation  already  mentioned.  As  the  tractus  cortico-olfactorius 
septi,  it  was  first  seen  to  appear  in  the  reptiles;  the  greatest  part  of  its 
course  is  visible  in  Fig.  144.  In  the  higher  mammals  and  in  man  the  tract 
is  not  to  be  recognized  without  further  study,  and  by  no  means  as  readily 
as  in  the  brain  of  the  marsupial,  shown  in  Fig.  123.  Nevertheless,  Zucker- 
kandl  has  succeeded  in  demonstrating  its  existence  in  an  entirely  satisfactory 
manner,  and  this  wholly  independently  of  the  more  recent,  comparative  ana- 
tomical considerations.  He  has  named  it  the  olfactory  bundle  of  the  cornu 
Ammonis. 


Fig.  143. — Median  sagittal  section  through  the  brain  of  a  calf.     The  lobus 
limbicus  is  shown  somewhat  lighter. 


The  greater  portion,  at  all  events,  springs  from  the  medulla  of  the  olfactory 
field.  The  large  tract  of  fibers  arises  on  the  under  side  of  the  brain  in  the  cortex  of 
the  olfactory  areaa  then  turns  over  this  toward  the  median  line  (see  Figs.  141  and 
144)  and  passes  along  beneath  the  gyrus  subcallosus  (Figs.  133  and  135)  dorsally, 
up  to  the  septum  pellucidum.  In  the  septum  a  part  of  the  fibers  cross  and  another 
part  goes  directly  backward.  Both  bundles,  reunited,  meet  with  the  fornix  at  the 
posterior  margin  of  the  septum  and  run  farther  backward  in  it  as  far  as  the  medulla 
of  the  cornu  Ammonis. 

For  that  which  follows,  compare  especially  Fig.  144. 

The  olfactory  lobe  and  the  olfactory  field  have,  in  the  main,  received 
the  afferent  tracts,  the  olfactory-nerve  pathways  of  the  second  order,  from 


218  AXATOilY    OF    THE    CENTBAL    XEEVOUS    SYSTEM. 

the  bulbus  olfactorius.  It  has  been  learned  in  earlier  chapters  that  both  of 
these  brain-parts  are  everywhere  present,  from  the  fishes  on  upward. 

The  lobus  pyriformis  and  the  cornu  Ammonis  are,  indeed,  parts  which 
are  connected  with  the  olfactory  apparatus;  nevertheless,  they  are  character- 
ized by  their  structure  as  immense  separate  territories  which  are  able  of 
themselves  to  bring  about  the  most  manifold  associations,  etc. 

They  are  most  probably  the  cortical  areas  of  smell;  their  very  large 
development  also  argues  in  favor  of  this. 

Let  us  now  examine  more  closely  what  tracts  they  receive  and  what 
others  they  give  origin  to.  .  ' 

The  cortical  area  of  smell  receives  its  tracts,  on  the  one  hand,  through 
the  olfactory  bundle;  on  the  other,  through  the  fibers  running  superficially 
in  the  layer  of  tangential  fibers.  But  what  tracts  does  it  send  out?  These 
collect  at  its  mesial  edge  as  the  firribria  (Fig.  143),  and  then  pass  toward  the 
anterior.  It  is  soon  recognized  that  they  belong  to  at  least  two  different  sys- 
tems. A  large  part  separates  at  the  anterior  end  of  the  gyrus  hippocampi, 
and  even  somewhat  farther  posteriorly  also,  and  passes  over  to  the  cornu 
Ammonis  of  the  other  side.  These  connecting  fibers,  in  their  entirety,  are 
called  the  psalterium.  These  are  the  mesially-lying  fibers.  From  the  more 
lateral  fibers,  however,  another  bundle  is  collected.  Tracts,  directed  for 
the  most  part  longitudinally,  here  pass  forward  and  run  for  a  short  distance 
next  to  the  olfactory  bundle,  entering  at  this  point,  but  soon  leave  it  again 
to  pass  backward  in  a  downward-directed  course.  These  are  the  fornix. 
It  ends  near  the  base  of  the  brain  in  the  corpus  mamillare  and  also  in  the 
opposite  thalamus.  The  fornix  is  consequently  that  part  of  the  medulla  of  the 
gyrus  hippocampi  which,  not  used  for  commissures,  connects  this  medulla  with 
the  interbrain.  With  the  "descending  fornix,"  as  that  part  is  called  in  con- 
tradistinction to  the  bundle  running  longitudinally  forward  from  the  cornu 
Ammonis — the  "ascending  fornix" — there  is  associated,  however,  another 
tract  of  fibers  which  arises  from  that  part  of  the  marginal  gyrus  that  is  not 
inrolled  to  form  the  cornu  Ammonis,  the  gyrus  limbicus.  In  order  to  reach 
down  to  the  fornix  its  tracts  must  pass  through  the  corpus  callosum,  which 
always  covers  over  the  ventricle  in  mammals.  The  bundle  is  called  the 
fornix  longus.  Its  fibers  always  lie  just  under  the  corpus  callosum  and  an- 
teriorly, forming  the  most  mesial  bundles  of  the  pillar  of  the  fornix;  they 
pass  down  with  this  to  the  bottom  of  the  interbrain. 

It  is  very  probable  that  the  descending  fornix,  as  well  as  the  fornix 
longus,  receives  in  its  course  fibers  from  the  opposite  olfactory  cortex  by 
way  of  the  psalterium. 

In  the  smaller  mammals  the  relations  of  the  fimbria  and  the  psalterium,  as  well 
as  of  the  fornix.,  are  better  known  than  in  man.  This  is  because,  on  the  one  hand, 
they  are  relatively  much  larger  structures  in  the  osmatic  animals  investigated  than 


220  ANATOMY    OF   THE    CENTRAL    NERVOUS    SYSTEM. 

in  man;  on  the  other,  because  Giiddcn,  with  a  masterly  hand  for  experimentation, 
was  able  to  throw  abundant  light  on  this  very  region  of  the  anatomy  of  the  fornix 
by  experiments  on  animals. 

The  fornix  longus  has  been  demonstrated  in  man   only  recently  by  Kolliker. 

In  many  of  the  smaller  animals  the  fibers  of  the  psalterium,  the  decussations  in 
it,  the  decussation  of  the  fornices  longi,  and  the  crura  fornicis  at  their  turning-point 
into  the  depths  of  the  central  gray  matter,  together  form  a  single  thick  mass,  which 
has  been  designated  as  the  corpus  fornicis. 

The  olfactory  lobe  and  the  hippocampal  lobe  possess,  in  addition  to 
those  mentioned,  a  number  of  tracts  that  are  fitted  to  connect  them  with 
one  another  or  with  other  regions.  Thus  there  runs  dorsally  on  each  side 
of  the  median  line  of  the  corpus  callosum  along  its  entire  length  a  delicate 
bundle  of  large  fibers,  the  stria  longitudinalis  medialis,  which,  arising  in  the 
dorsal  regions  of  the  hippocampal  cortex,  curves  down  anteriorly  over  the 
corpus  callosum  and  radiates  into  the  septum  pellucidum.  Then  it  is  known 
that  a  long  bundle,  the  cingulum,  running  in  the  gyrus  fornicatus  sends 
tracts  into  the  olfactory  cortex,  as  well  as  into  the  other  parts  of  the  mar- 
ginal gyrus. 

All  these  tracts  belong  to  the  cortical  centers  of  the  olfactory  apparatus. 
There  are,  however,  connections  between  the  olfactory  apparatus  and  the 
interbrain  which  must  be  very  important,  because  they  are  well  developed 
in  all  animals,  even  in  those  without  a  cerebral  cortex,  and  are  everywhere 
demonstrable.  In  order  to  understand  them,  we  must  return  again  to  the 
medulla  of  the  lobus  olfactorius.  It  is  known  that  this  arises,  for  the  most 
part,  from  the  bulbus.  Posteriorly  it  continues  directly  into  the  medulla 
of  the  olfactory  field.  We  have  already  become  acquainted  with  one  con- 
necting tract  of  this  "deep  olfactory  medulla":  the  olfactory  bundle  to  the 
cornu  Ammonis. 

The  olfactory  medulla  possesses  at  least  two  other  connections.  One 
of  these  tracts,  consisting  essentially  of  fine  fibers,  runs  backward  .and  can 
be  followed  as  far  as  into  the  region  of  the  corpus  mamillare.  In  its  course  it 
must  pass  through  the  most  ventral  regions  of  the  corpus  striatum;  but  it 
receives  no  fibers  from  this — as  has  been  supposed. 

Certain  of  these  fibers  proceed  still  farther  posteriorly,  as  far  as  into  the  region 
of  the  ganglion  interpedunculare;  perhaps  into  the  fillet  also. 

A  second  tract,  originating  essentially  from  the  lateral  parts  of  the 
medulla  of  the  olfactory  area  and  passing  through  the  forepart  of  the  thala- 
mus,  rises  to  the  inner  surface  of  the  ventricle,  and  passes  along  this,  back- 
ward to  the  ganglion  habenulas.  It  is  the  tcenia  thalami. 

In  a  dog's  brain,  in  which  the  entire  cerebral  cortex  had  been  removed  eighteen 
months  before  death  and  the  entire  radiation  from  the  mantle  was  wanting  as  a 


THE    BRAIX    OF    MAMMALS    AND   THE    OLFACTOEY   APPARATUS.          221 

consequence,  the  cortex  of  the  olfactory  area  alone  remained  intact.  From  this,  the 
olfactory  radiation  could  be  traced  backward  very  clearly  and  distinctly  to  the  corpus 
mamillare  and  upward  as  the  teenia  thalami  to  the  ganglion  habenulse.  The  fibers 
must  have  their  origin  in  the  olfactory  field  itself,  for  the  taenia  was  not  degen- 
erated, although  the  fibers  had  accidentally  been  badly  injured  just  in  front  of  the 
ganglion  habenulte  on  both  sides  during  the  operation. 

The  olfactory  fibers  have  thus  been  followed,  on  the  one  hand,  as  far 
as  into  the  cerebral  cortex,  and,  on  the  other  hand,  as  far  as  into  the  ganglion 
habennlae  and  into  (?)  the  corpus  mamillare.  It  will  be  seen,  later,  that 
still  other  ganglia  of  the  midbrain  and  interbrain  stand  in  intimate  connec- 
tion with  these  ganglia. 

In  mammals  (Lotheissen)  fibers  from  the  fornix  also  mix  with  those  of 
the  tsenia  thalami,  exactly  as  in  reptiles  (see  above). 

The  entire  olfactory  apparatus  thus  appears  as  a  huge  complex  of 
ganglia  and  bundles  running  through  the  greater  part  of  the  brain.  In  the 
subsequent  chapters  its  separate  parts  will  be  constantly  met  with. 

It  has  been  seen  that  a  not  inconsiderable  portion  of  the  surface  of  the 
brain  owes  its  perfection  essentially  to  the  development  of  the  olfactory  ap- 
paratus. All  the  gyri  and  tracts  belonging  to  this  are  constantly  demon- 
strable in  the  same  place  and  in  a  similar  relation. 

The  development  of  the  remaining  portion  of  the  mantle  and  the  fis- 
sures running  in  it  is  much  less  constant.  You  will  remember  that  the 
development  of  the  brain  is  limited  by  other  factors  than  those  of  the 
cranium,  that  the  presence  and  the  course  of  the  fissuration  is  determined  by 
the  resultant  of  at  least  two  different  developmental  tendencies,  as  has  been 
explained  in  the  preceding  chapter. 

Fissures  that  are  deep  and  long  in  man  may  be  entirely  wanting  in 
closely  related  animals;  others,  only  suggested  in  man,  are  at  times  well 
developed  in  animals. 

In  some  mammals,  the  fissura  Sylvii,  for  example,  one  of  the  fissures 
most  frequently  present,  is  not  present  at  all  or  indicated  by  a  shallow  sulcus 
only.  The  other  sulci  may  assume  the  most  various  directions.  In  general, 
however,  it  may  be  recognized  that  there  are  essentially  three  principal 
directions:  fissures  running  parallel  with  the  longitudinal  fissure,  sagittal; 
fissures  curving  around  the  Sylvian  fissure,  fissurce  arcuatce ;  fissures,  finally, 
of  a  more  or  less  vertically  ascending  type,  fissura;  coronales.  In  the  human 
brain  the  central  sulcus  is  a  good  example  of  the  last;  sagittal  sulci  traverse 
the  frontal  lobe,  and  arcuate  sulci  surround  the  Sylvian  fissure  in  the  tem- 
poral and  parietal  lobes.  It  is  precisely  the  vertical  fissures  which  are  in 
most  cases  but  feebly  developed  in  animals.  On  the  bear's  brain  (Fig.  145) 
the  central  fissure  is  certainly  relatively  long.  Make  use  of  this  well-known 


222  ANATOMY   OF    THE    CENTRAL    NERVOUS    SYSTEM. 

fissure,  in  order  to  facilitate  the  comparison  with  the  human  brain.  The 
frontal  lobe,  lying  in  front  of  it,  is  seen  to  be  very  much  less  developed  than 
in  Fig.  130.  It  is  difficult  to  homologize  the  frontal  sulci.  The  central 
fissure  runs  more  vertically,  probably  on  account  of  the  imperfect  develop- 


Fig.  145. — Brain  of  a  bear.     The  frontal  lobe  is  shaded.     (Aft«r  Turner.) 

ment  of  the  frontal  lobe;  likewise  all  the  parts  lying  behind  it  are,  in  a 
measure,  pushed  upward,  the  fissura  Sylvii  standing  almost  vertically.  Ar- 
cuate fissures  surround  the  fissura  Sylvii,  on  which,  upon  comparison  with 
Fig.  130,  a  similar  arrangement  is  readily  recognized  after  a  moment's  con- 


Fig.  146. — Brain  of  the  narwhal:    Monodon  monoceros.     (After  Turner.) 

sideration:  how  these  pass  over  into  the  temporal  sulci  and  the  interparietal 
fissure. 

The  Sylvian  fissure  is  more  vertical  in  all  animal  brains  than  in  that  of 
man;  it  is  more  horizontal  the  more  the  frontal  lobe  is  developed.  It  is 
commonlv  relativelv  short. 


THE    BRAIN    OF    MAMMALS    AND    THE    OLFACTORY   APPARATUS. 


223 


In  the  vertebrate  series  arcuate  fissures  occur  more  frequently  than  any 
other.  On  the  richly  convoluted  brain  of  the  narwhal  they  form  the  type  of 
the  entire  fissuration  (Fig.  146). 

They  are  numbered,  counting  from  the  Sylvian  fissure  out,  as  the  first, 
second,  etc.,  arcuate  fissure,  or  they  are  also  named  as:  fissura  ectosylvia, 
fissura  suprasylvia,  etc.  On  the  brain  of  the  dog,  which  here  follows,  a 
number  of  these  fissures  are  again  recognized  from  the  form  and  the  loca- 
tion. At  the  posterior  boundary  of  the  frontal  lobe  a  short  sulcus  passes 
downward  in  a  vertical  course:  the  fissura  cruciata.  It  probably  corresponds 
to  the  fissura  centralis;  yet  the  identity  of  the  two  fissures  is  not  undisputed. 
As  was  mentioned  in  the  second  chapter,  the  brains  of  many  animals  are 
entirely  smooth.  On  others  there  are  found  only  slight  indications  of  sulci. 
On  many  brains — for  example,  those  of  the  horse  and  the  cow — the  arcuate 
type  is  only  distinct  in  the  territories  lying  next  to  the  Sylvian  fissure — 
toward  the  edge  of  the  brain  the  fissures  have  a  more  sagittal  course.  It 


Fig.  147. — Brain  of  a  dog.     The  frontal  lobe  is  shaded. 


would  be  too  much  of  a  digression  to  mention  what  is  at  present  known  con- 
cerning the  direction  of  the  sulci  in  the  various  classes  of  animals.  The 
examples  given  are  only  intended  to  illustrate  certain  types  and  to  serve  as 
an  introduction  to  studies  of  your  own. 

Our  knowledge  of  the  course  of  the  convolutions  of  the  brain  comes  from  the 
investigations  of  Bnrdach  (median  surface),  Letiret,  Gratiolet,  Meynert  (comparative 
anatomy),  Bischoff,  Ecker,  and  Pansch  (growing  and  adult  brain).  Moreover,  there 
exist  numerous  investigations  on  separate  regions  of  the  brain:  on  the  gyri  running 
near  the  margin  of  the  brain  by  Broca  and  Zuckerkandl ;  on  the  frontal  gyri  by 
EberstaUer  and  by  Herrt ;  on  the  insula  by  Guldberg  •  further,  accurate  studies  on 
the  development  and  course  of  single  fissures  by  Riidinger,  Cunningham,  and  others. 
Besides  this  we  possess  very  many  monographs  on  the  brain-surface  of  various  mam- 
mals; on  anthropoid  apes  by  Bischoff,  Waldeyer,  and  others;  on  lemurs  by  Flower 
and  Gervais ;  on  whales  by  Guldberg,  Ziehen,  and  Kiikenthal ;  on  ungulates  by 
Krueg,  Ellenbergcr,  TcncJiini,  and  Negrini;  on  carnivorous  animals  by  Meynert, 


224: 


ANATOMY    OF    THE    CENTRAL    NERVOUS    SYSTEM. 


Spltzka,  and  others.  For  recent  compilations,  criticisms,  and  comparisons,  we  are 
especially  indebted  to  Turner,  then  to  Ziehen  and  Kiikenthal.  The  numerous  varia- 
tions from  the  type  described,  whether  they  may  exist  normally  or  on  account  of 
malformations,  have  received  consideration  from  most  of  the  above-mentioned  au- 
thors, but  particularly  from  Ricliter,  Sernow,  and  others. 

For  the  olfactory  apparatus,  the  older  investigations  of  Meynert,  Ganscr,  Bevan 
Lewis,  and  others,  are  the  foremost.  The  description  given  in  the  text  follows  per- 
sonal investigations  made  in  common  with  Dr.  Flatow.  More  recent  important  re- 
searches come  from  Kolliker  and  from  Lowenthal  ("degeneration"  experiments). 
Finally  it  must  be  emphasized  at  this  point  that,  as  the  excellent  investigations  of 
Elliott  Smith  show,  the  brains  of  the  marsupials  and  the  monotremes  present  espe- 
cially clear  and  simple  relations  for  the  central  olfactory  apparatus. 

A  perusal  of  the  work  of  this  investigator  is  particularly  recommended. 

It  does  not  lie  within  the  scope  of  this  text-book  to  impart  the  rich  store  of 


Fig.  148. — The  projection  areas  of  the  cortex  at  present  known. 


facts  concerning  the  functions  of  the  separate  parts  of  .the  brain  which  pathology  has 
ascertained.  The  study  of  the  function  of  the  cerebral  cortex  is  still  entirely  in  its 
infancy,  and  is  in  nowise  concluded.  It  may  be  said,  in  general,  that  more  is  posi- 
tively known  about  man  than  about  animals  concerning  the  phenomena  occurring 
after  injury  to  the  cortex.  The  following  comprehends  a  short  summary  only  of 
these  symptoms: — 

Injuries  that  involve  the  normal  structure  and  the  normal  function  of  the  cere- 
bral cortex  produce,  in  man,  different  symptoms,  according  to  the  place  where  they 
are  located.  Up  to  the  present  time,  several  hundred  carefully  observed  cases  of 
disease  of  the  cerebral  cortex  have  been  known,  and,  by  comparing  these  with  one 
another,  the  following  conclusions  may  be  arrived  at: — 

Motor  symptoms  of  irritation  (from  the  twitching  of  a  single  muscle  up  to 
epilepsy)  may  arise  from  any  point  of  the  cerebral  cortex.  There  exists  a  zone  of 


THE    BRAIN    OF    3IAMMALS   AXD    THE    OLFACTOEY   APPARATUS. 


225 


the  brain,  embracing  the  two  central  gyri,  after  disease  or  injury  of  which  disturb- 
ances in  motility  almost  always  appear  on  the  opposite  side  of  the  body.  These 
disturbances  are  divided  into  phenomena  of  irritation  and  phenomena  of  degenera- 
tion. The  symptoms  of  irritation  are  expressed  by  spasms  or  convulsive  movements; 
the  symptoms  of  degeneration  by  a  more  or  less  high  degree  of  inability  to  set  the 
muscles  in  motion  at  will,  oftentimes  only  in  a  sense  of  weakness,  or  by  awkward- 
ness in  executing  complicated  movements. 

From  an  accurate  analysis  of  the  known  cases  of  disease,  it  may  be  stated  that, 
in  disease  of  the  upper  part  of  both  central  gyri  and  of  the  paracentral  lobule,  the 
motor  disturbances  manifest  themselves  preponderantly  in  the  legs;  that,  if  the 
inferior  end  of  the  central  gyri  is  involved,  the  regions  of  the  facialis  and  the  hyp- 
oglossus  are  affected,  and  that  motor  disturbances  in  the  upper  extremity  especially 
may  be  produced  by  disease  of  about  the  middle,  and  a  portion  of  the  upper,  third 
of  these  gyri.  The  separation  of  the  "centers"  from  one  another  is  not  a  distinct  one. 

Complete  destruction  of  separate  parts  of  the  central  gyri  may  lead,  in  man,  to 
permanent  paralysis  of  the  muscles  connected  with  those  parts.  The  paralyzed  mus- 
cles almost  always  fall  into  a  state  of  contracture. 


Fig.  149. — The  cortical  areas,  as  far  as  they  are  demonstrable  by 
irritation.    A,  Cat.    B,  Rabbit.     (After  Mann.) 


Diseases  or  injuries  that  involve  the  cortex  of  the  left  inferior  frontal  gyrus  or 
the  left  insula  generally  lead  to  a  more  or  less  complete  loss  of  speech,  although  the 
vocal  organs  may  still  be  normally  innervated  and  the  patient  may  often  perfectly 
understand  all  that  is  said.  It  appears  that  the  ability  to  understand  whatever  is 
said  even  in  a  loud  voice  is  lost  if  the  superior  temporal  gyrus  is  affected.  The 
ability  to  comprehend  reading  has  been  repeatedly  seen  to  be  lost  after  lesions  of  the 
cortex  situated  between  the  apex  of  the  occipital  lobe  and  the  posterior  end  of  the 
Sylvian  fissure.  Perhaps  deep  tracts  are  here  involved,  and  it  is  not  a  question  of 
cortical  localization. 

Lesions  in  the  region  of  the  occipital  lobe  may  lead  to  disturbance  of  vision, 
manifested  as  a  dimness  of  vision  or  blindness  on  the  outer  side  of  the  eye  on  the 
affected  side  and  on  the  inner  side  of  the  other  eye  (see  below). 

The  preservation  of  the  cuneus  appears  to  be  especially  important  for  the  com- 
prehension of  what  is  seen. 

Sensibility  may  also  suffer  from  affections  of  the  cerebral  cortex.  Feelings  of 
numbness,  heaviness,  and  marked  disturbances  of  the  muscular  sense  are  frequently 


226  ANATOMY    OF    THE    CENTRAL    NERVOUS    SYSTEM. 

observed.  As  a  rule,  the  sense  of  touch  at  first  appears  to  be  blunted  so  far  as  the 
judgment  of  what  is  felt  comes  in  question,  but  very  slight  stimuli  may  be  recog- 
nized as  tactile  irritants  if  they  are  of  a  very  simple  nature  (as  touching  with  a 
downy  feather,  needle-point,  etc.).  Areas  of  the  cerebral  cortex  from  which  disturb- 
ances of  sensibility  arise  more  frequently  than  from  lesion  of  others  are  not  definitely 
known.  At  all  events,  such  disturbances  may  appear  after  lesions  situated  in  the 
territory  of  the  central  gyri  and  their  neighborhood.  It  is  very  probable  that  lesions 
of  the  cornu  Ammonis,  perhaps  of  the  remaining  parts  of  the  marginal  gyrus  also, 
may  produce  disturbances  in  the  sense  of  smell. 

The  paralyses  that  arise  from  affections  of  the  cerebral  cortex  alone  are  never 
so  complete  as  those  produced  by  the  destruction  of  the  peripheral  nerves  or  their 
proximal  ends  in  the  spinal  cord.  In  animals  it  is  generally  impossible  to  obtain 
permanent  paralyses  by  the  removal  of  the  cortex  in  the  motor  zone,  or  the  removal 
of  the  entire  portion  of  the  brain  that  contains  this  zone.  Nevertheless,  upon  irrita- 
tion of  circumscribed  areas  of  the  cerebral  cortex  in  these  same  animals  the  same 
muscles  may  nearly  always  be  made  to  contract  from  the  same  cortical  area. 

And  now,  having  become  acquainted  with  the  location  of  the  cortical  centers 
in  man,  let  us  cast  a  glance  at  the  illustrations  shown  in  Fig.  149.  They  show,  ac- 
cording to  the  experiments  of  Mann,  what  parts  of  the  surface  of  the  mammalian 
brain  are  at  present  known  to  have  a  definite  function. 

This  leads  us  back  to  what  was  said  in  the  twelfth  chapter  respecting  the  sig- 
nificance of  the  mantle  as  a  collection  of  individual  centers  and  areas  of  associa- 
tion. It  is  immediately  recognized  that  much  that  is  found  in  the  brain  of  Primates 
is  not  present  at  all  in  the  lower  mammals,  or  is  so  small  as  not  to  be  demonstrable. 

For  a  better  understanding  of  the  physiological  status  of  the  mantle  of 
the  brain,  consider  again  what  was  presented  on  page  173,  and,  moreover, 
recollect  the  experiments  of  Ewald,  mentioned  on  page  44.  These  show 
that  many  things  are  necessary  for  the  orderly  execution  of  the  acquired 
movements,  and  that,  where  lesions  exist,  one  factor  or  another  may  occa- 
sionally compensate  for  what  was  lost. 

It  may  truly  be  said  that  the  mantle  of  the  brain  increases  in  mass  as, 
ascending  in  the  vertebrate  series,  new  centers  are  established  in  it:  cortical 
areas  that  are  concerned  in  the  execution  of  movements  for  the  inhibition, 
recognition,  and  interpretation  of  sensory  impressions,  and,  probably  in  a 
large  measure,  for  association  also. 


CHAPTER   XV. 

THE  CORTEX  OF  THE  FOREBRAIN  AND  THE  MEDULLA  OF  THE  HEMI- 
SPHERES ;    THE  COMMISSURES  AND  THE  CORONA  RADIATA. 

A  GENERAL  survey  has  now  been  attained  of  the  outer  form-relations 
of  the  brain.  The  present  chapter  is  intended  to  familiarize  you  with  the 
structure  of  the  cerebral  cortex  and  to  give  an  insight  into  the  mode  of  con- 
nection of  the  cortical  regions  with  one  another  and  with  the  deeper-lying 
structures. 

The  finer  structure  of  the  cortex  is  known  in  its  elements  only.  Knowl- 
edge of  the  combinations  of  these  elements  with  one  another  is  still  wanting, 
and  therewith,  unfortunately,  a  proper  understanding  of  the  anatomical 
basis  of  the  great  organ  of  the  mind.  There  is  hardly  a  doubt  but  that  the 
cerebral  cortex,  as  a  whole,  may  be  regarded  as  the  place  where  most  of 
those  cerebral  processes  take  place  which  arise  in  consciousness,  that  it  is  the 
seat  of  memory,  and  that  the  voluntary  acts  proceed  from  it. 

The  entire  hemisphere  is  covered  by  the  cortex.  This  has  not,  how- 
ever, exactly  the  same  structure  everywhere  on  the  convexity.  Even  if  a 
sort  of  fundamental  type  exists,  greater  or  lesser  differences  in  the  layers, 
in  which  the  ganglion-cells  and  nerve-fibers  are  arranged,  may,  nevertheless, 
be  found,  depending  on  the  region  of  the  brain  investigated.  One  cortical 
type  never  passes  abruptly  over  into  another.  Inasmuch  as  the  significance 
of  these  anatomical  variations  is  not  understood,  one  region  only,  the  frontal 
lobe,  will  be  considered  at  present. 

A  dense  net-work  of  fine,  medullated  fibers,  mostly  running  parallel  with 
the  surface,  lies  close  under  the  pia,  but  is  separated  from  it  by  a  thicker 
layer  of  neuroglia.  It  is  the  layer  of  tangential  fibers  (Fig.  150).  Cells  are 
distributed  in  it  in  relatively-small  quantity.  Directly  beneath  it,  however, 
begins  the  layer  of  the  pyramidal  cells — cells  distinctly  typical  of  the  cortex. 
They  appear  first  as  a  layer  of  numerous  smaller  elements  (2,  Fig.  150), 
which  passes  over  into  the  layer  of  the  large  pyramids  (3,  Fig.  150).  All 
of  these  cells  send  their  dendrites  toward  the  surface  of  the  cortex  and  in 
various  other  directions,  as  the  apical  process,  lateral  processes,  etc.,  and,  for 
the  most  part,  send  their  neuraxons  deep  down  into  the  medullary  layer. 
The  layer  of  the  large  pyramidal  cells  in  the  frontal  and  parietal  lobes  is  the 
broadest  in  section  of  any  of  the  cortical  layers  of  these  lobes.  The  in- 

(227) 


228 


ANATOJIY    OF    THE    CENTRAL    NERVOUS    SYSTEM. 


dividual  cells  are  larger 
and  their  apical  proc- 
esses longer,  the  farther 
the  cells  lie  from  the  sur- 
face. The  fourth  layer 
of  cells,  lying  beneath 
the  large  pyramids,  con- 
sists again  of  smaller 
cells,  not  uniformly  dis- 
tributed. They  are 
wedged  in  between  the 
radiating  masses  of  med- 
ullated  fibers  passing 
into  the  cortex. 

Besides  the  pyramidal 
cells  mentioned,  there  is 
scattered  in  all  layers 
of  the  cortex  a  large 
quantity  of  smaller, 
polygonal  cells,  the  neu- 
raxons  of  which  split  up 
completely  very  soon 
after  leaving  the  cell. 

In  Fig.  150  these  cells 
appear  as  numerous, 
clear,  polygonal  struct- 
ures lying  everywhere  in 
the  neighborhood  of  the 
pyramids. 

In  order  to  become 
acquainted  with  the  his- 
tology of  the  cortex,  it  is 
necessary  to  employ  sev- 
eral methods.  Each 
shows  a  different  pict- 
ure, and  only  by  com- 
bining these  is  there  ob- 
tained an  accurate  con- 
ception of  it  as  a  whole. 
Since  a  small  part  only 
of  the  cells  is  visible 
in  Fig.  151  (left  side), 


CORTEX    OF    FOREBRAIX    AND    MEDULLA    OF    HEMISPHERES. 


229 


a  section  is  here  shown  in  Fig.  150 
accurately  reproduced  by  Nissl  from 
an  alcoholic  preparation.  It  may  be 
of  good  use  to  you  in  practical 
work. 

The  medullary  rays  separate,  011 
reaching  the  cortex,  into  numerous 
fine  tracts,  and  these  become  gradually 
lost  in  the  more  superficial  layers  of 
the  cortex;  that  is  to  say,  become  con- 
nected with  the  neuraxons  of  the  cells. 
Besides  these  tracts,  numerous  other 
medullated  nerve-fibers  are  seen  in  the 
cortex.  Until  recently  the  origin  and 
destination  of  these  fibers  were  entirely 
unknown.  Lately,  however,  the  in- 
vestigations by  Golgi,  Martinotti,  and 
especially  by  S.  Ramon  y  Cajal,  have 
acquainted  us  with  a  great  number  of 
new  relations  in  the  cerebral  cortex;  so 
that  it  now  appears  possible  to  consider 
the  separate  elements  in  their  various 
combinations.  It  is  true,  most  of  the 
facts  have  been  recognized  on  the  cere- 
bral cortex  of  small  mammals,  and  a 
few  only  have  been  confirmed  for  man. 
Thus,  much  work  still  remains  to  be 
done.  "What  is  known,  however,  takes 
us  such  a  good  step  forward  that  I 
must  impart  it  to  you.  In  order  that  I 
might  make  my  description  brief,  I 
have  represented  the  most  important 
discoveries  combined  in  a  single  draw- 
ing (Fig.  152). 


Fig.  151. — Section  through  the  cortex  of  a  frontal  gyrus.  The  right  half  is 
reproduced  from  a  preparation  stained  with  Weigert's  haematoxylin,  the  left  half 
from  preparations  made  by  Golgi's  sublimate  method.  On  the  right  the  fibers 
only  are  to  be  seen;  on  the  left  the  cells  only.  More  cells  are  present  than  are 
shown  in  the  drawing.  Since  the  spaces  around  the  cells  and  their  processes 
are  filled  by  Golgi's  method,  these  appear  to  be  larger  than  they  really  are. 
Tangential  fascrn.  Tangential  fibers.  Superradiares  FlccJttirerk.  Superradial  net- 
work. GennariscJier  Streif,  Line  of  Gennari.  Interradiares  Flechtwerk,  Inter- 
radial  net-work. 


Fig.  152. — Section  through  the  cerebral  cortex  of  a  mammal.     (Combined 
from  preparations  by  S.  Ram6n  y  Cajal.) 


CORTEX    OF   FOREBRAIN   AND   MEDULLA   OF   HEMISPHEEES.  231 

The  outermost  layer  contains  numerous  nerve-fibers  running,  for  the  most  part, 
in  a  tangential  direction.  These  arise  from  ganglionic  cells  (a,  ft,  and  C),  all  of 
which  possess  several  neuraxons,  and  from  small  fusiform  cells  (d)  of  a  deeper  layer. 
Two  kinds  of  elements  enter  this  outermost  zone.  Large  fibers  (e),  mostly  medullated, 
which  pass  into  the  cortex  from  the  medullary  layer,  are  traced  in  their  outermost 
ramifications  into  this  layer.  They  must  originate  from  ganglionic  cells  that  lie 
in  other  parts  of  the  brain.  The  caliber  of  the  fibers  speaks  especially  for  a  distant 
origin.  Then  the  dendrites  of  the  more  deeply  situated  pyramidal  cells  (f)  end  in  this 
layer  in  dense,  profuse  ramifications.  Numerous  fine  secondary  twigs,  terminating  in 
little  knobs,  project  from  each  of  the  small  branches.  The  ramification  is  so  dense 
that  exceedingly  abundant  opportunity  is  afforded  for  the  contact  of  the  dendrites 
of  deep  cells  with  similar  dendrites  and  the  neuraxons  of  cells  lying  in  this  locality. 
Even  the  most  daring  phantasy  of  speculative  psychologists  has  hardly  allowed  itself 
to  imagine  such  an  abundance  of  possible  combinations  as  has  here  been  revealed 
of  the  dendrites  with  neuraxons  of  cells  which  have  very  different  locations. 

And,  moreover,  every  cell  is,  and  remains,  an  independent  individual,  not  here 
only,  but  everywhere  else  in  the  cortex.  Direct  union  is  nowhere  recognized;  con- 
nection by  contact  alone  is  observed  throughout. 

The  layer  of  small  pyramidal  cells  lies  under  the  layer  of  tangential  fibers. 
It  passes  very  gradually  over  into  the  layer  of  the  large  pyramids  (3).  The  neu- 
raxons of  all  these  cells  pass  in  a  direction  toward  the  medullary  layer;  they  give 
off  numerous  collaterals.  Many  neuraxons  divide  near  the  medullary  layer  into  a 
horizontal  and  a  descending  branch.  From  these  fibers  arise  the  tracts  which  con- 
nect the  cerebral  cortex  with  deeper-lying  centers  and  which  connect  distant  cortical 
centers  with  one  another. 

The  dendrites  extend  a  greater  or  less  distance  out  toward  the  periphery,  and 
some  of  them  end  only  under  the  pia. 

Near  the  medullary  layer,  below  the  well-defined  pyramids,  lie  numerous  irregu- 
larly triangular,  also  small  pyramidal,  cells.  As  regards  the  course  of  their  neu- 
raxons, as  well  as  their  dendrites,  they  are  analogous  to  the  pyramids,  but  they 
present  more  irregular  forms  and  a  less  dense  ramification.  In  this  deepest  layer  are 
found  numerous  multipolar  cells  (g) ,  the  neuraxons  of  which  may  run  in  the  most 
various  directions:  horizontal,  ascending,  descending,  etc.  The  neuraxon  is  always 
characterized  by  the  fact  that,  after  a  short  course,  it  breaks  up  into  a  wide,  com- 
plicated arborization,  the  terminal  fibrils  of  which  all  end  freely.  Moreover,  such 
cells  are  also  present  in  almost  all  of  the  other  layers  of  the  cortex.  With  their 
extensive  ramification,  they  are  well  adapted  to  connect  other  cell-groups  with  one 
another  physiologically. 

The  innumerable  neuraxons  with  their  collaterals  and  the  numerous 
fibers  passing  into  the  cortex  from  other  parts  of  the  brain  together  form, 
as  would  be  expected,  an  extraordinarily  dense  net-work.  It  was  only  pos- 
sible to  untangle  this  complex  through  the  happy  circumstance  that  the 
method  of  Golgi  always  impregnates,  at  the  most,  relatively  few  cells  in  any 
one  section.  The  same  net-works  of  fibers,  as  shown  in  Fig.  151  by  the 
myelin-staining  method,  may  be  demonstrated  with  the  staining  of  the  cells, 
but  in  the  latter  case  they  are  much  more  compact  and  solid.  It  appears 
that  the  neuraxons  of  most  of  the  cells  in  the  cortex,  and  the  collaterals,  also, 
which  arise  from  the  neuraxons  of  the  pyramids,  possess  a  medullary  sheath. 


232 


ANATOMY    OF    THE    CENTRAL    NERVOUS    SYSTEM. 


So  long  as  we  are  unable  correctly  to  name  all  of  these  fibers  according  to 
their  function,  it  will  be  advantageous,  for  the  sake  of  clearness, — e.g.,  in 
investigations  in  pathology, — to  introduce  provisional  names  for  them. 

Let  us  distinguish  (1)  the  radii,  medullary  rays;  (2)  the  interradial 
net- work,  consisting  mostly  of  fibers  running  parallel  with  the  surface;  (3) 
the  superradial  net- work,  and  (4)  the  tangential  fibers.  Along  the  boundary 
between  the  superradial  and  the  interradial  net-works,  the  latter  becomes 
greatly  thickened.  This  layer,  everywhere  visible  to  the  naked  eye  as  a 
white  line,  is  so  much  thicker  in  the  region  of  the  cuneus  that  it  is  there 


Fig.  153. — Three  sections  through  the  cortex  of  the  anterior  central  gyrus. 
A,  From  a  child  1  V«  years  old.  B,  From  a  man  36  years  old.  C,  From  a  man 
of  53  years.  Myelin  staining.  Controls  have  shown  that  the  differences  are 
essentially  occasioned  by  the  age.  Yet  the  possibility  that  a  different  amount  of 
use  of  the  cortical  region  under  discussion  may  have  added  in  some  degree  to 
the  difference  cannot  be  overlooked.  (After  Kaes.) 


very  easily  recognized.  It  is  designated  as  the  line  of  Gennari,  or  after  its 
later  describers  as  the  line  of  Baillarger,  or  the  line  of  Vicq  d'Azyr  (in  the 
cuneus  particularly).  In  the  occipital  lobe,  however,  the  line  lies  somewhat 


COBTEX    OF    FOREBRAIN   AND   MEDULLA    OF   HEMISPHERES.  233 

deeper  in  the  third  layer,  nearer  to  the  fourth,  and  not  so  high  up  as  is  shown 
for  the  frontal  lobe  in  Fig.  151. 

The  medullated  fibers  in  the  superradial  net-work  probably  come,  for 
the  most  part,  from  fibers  radiating  into  the  cortex  from  without.  It  is  very 
questionable  whether  the  cells  with  the  short,  branched  neuraxons  have 
medullated  processes.  The  line  of  Gennari  is  formed  entirely  by  the  col- 
laterals of  the  neuraxons  from  the  pyramidal  cells.  The  interradial  net- 
work consists  likewise  of  the  collaterals  from  the  neuraxons  of  the  pyramidal 
cells,  and  perhaps  also  of  the  arborization  formed  by  the  cells  with  the  short, 
branched  neuraxons. 

It  must  not  be  expected  that  these  lines,  etc.,  will  be  found  uniformly 
well  developed.  Disregarding  the  fact  that  they  are  variously  well  defined, 
according  to  the  zone  of  the  cortex,  developmental  investigations  also  show 
that  very  considerable  differences  may  exist  according  to  the  age.  Probably 
it  will  be  proved,  when  we  at  last  recognize  a  fixed  type  for  all  the  parts  of 
the  cortex  and  all  ages  of  life,  that  definite  relations  exist  between  the  in- 
telligence of  the  individual  and  the  number  of  fibers  in  his  cortex. 

The  discoveries  of  Kaes  along  these  lines  are  promising  much.  He  was 
able  to  show  by  means  of  numerous  accurate  measurements  that  the  cerebral 
cortex  increases  in  richness  of  fibers  for  a  long  time,  even  to  the  fortieth  year 
and  longer.  Tracts  come  particularly  under  consideration  that  pass  along 
within  the  basal  portion  of  the  medullary  rays  in  a  direction  parallel  with 
the  surface,  fibra?  arcuate  intracorticales,  and  then  tracts  of  fibers  which, 
lying  within  the  superradial  net-work,  follow  closely  on  the  layer  of  tan- 
gential fibers.  Medullation  occurs  here  very  late  in  some  portions  of  the 
cortex;  so  that  a  very  great  part  of  the  cortex  below  the  layer  of  tangential 
fibers  is  gradually  traversed  by  delicate  fibers.  According  to  Kaes,  still 
larger  medullated  fibers  are  added  to  these,  which,  in  the  course  of  years, 
are  seen  to  extend  very  gradually  toward  the  surface  of  the  cortex  from  the 
layers  lying  next  to  the  medulla.  It  is  probably  the  fibers  of  this  plexus, 
some  very  large,  which  Bechterew  has  described  and  by  which  he  saw  formed 
a  distinct  line  lying  just  beneath  the  layer  of  tangential  fibers:  Bechterew'' 's 
line.  Fig.  153,  which  I  owe  to  the  kindness  of  Dr.  Kaes,  illustrates  well  the 
different  types  of  cortex  and  at  different  times  of  life. 

As  far  as  can  be  seen  at  present,  these  are  all  new  association-pathways, 
or  at  least  pathways  which,  only  called  into  use  late  in  life,  become  medul- 
lated at  a  late  period.  It  is  possible,  also,  that  we  are  concerned  with  col- 
laterals, which,  with  the  greater  demand  consequent  upon  increased  asso- 
ciations, now  attain  their  complete  development:  the  formation  of  the 
medullary  sheath.  It  is  known  that  in  other  tissues  also  an  acceleration  of 
growth  may  occur,  owing  to  an  increased  demand  made  upon  the  elements. 
Thus,  the  similar  process  in  the  cerebral  cortex  should  present  nothing  that 


234  ANATOMY    OF   THE    CENTRAL   NERVOUS    SYSTEM. 

deviates  from  the  known  phenomena.  It  may  well  be  imagined  that  man 
creates  new  pathways  for  himself  by  cerebral  activity,  in  the  sense  that  the 
new  formation,  or  the  strengthening  of  pathways  already  present,  may,  as 
the  anatomical  basis,  correspond  to  the  increased  ability  for  execution  which 
exercising  of  the  brain  produces. 

As  has  been  previously  mentioned,  the  cerebral  cortex  is  not  similarly 
constructed  at  all  points  of  the  surface.  The  cortex  in  the  neighborhood  of  the 
fissura  calcarina,  for  example,  is  characterized  by  a  preponderance  of  the 
small  polygonal  cells  (most  of  which  are  clearer)  and  by  a  relative  poverty 
of  the  large  pyramidal  cells,  in  addition  to  the  line  of  Gennari. 

The  conformation  of  the  cornu  Ammonis  deserves  special  consideration. 
Near  the  median  line  at  the  base  of  the  brain,  the  cortex  first  turns  out- 
ward, then  directly  inward  again,  and  then  curves  outward  again  for  a 
short  distance  (see  Fig.  154).  The  pyramidal  cells  of  the  gyrus  hippo- 
campi, however,  do  not,  as  a  consequence,  pass  over  immediately  into 
those  of  the  gyrus  dentatus.  They  end,  rather,  by  being  irregularly  grouped 
together  (at  a  in  Fig.  154),  and  this  irregular  mass  is  then  surrounded  by 
the  semicircle  of  regularly  arranged  cells  of  the  gyrus  dentatus.  We  are 
now  able,  without  difficulty,  to  trace  the  layers  of  the  eornu  Ammonis  back 
to  the  typical  layers  of  the  cortex  (Meynert  and  especially  8 chaffer).  Never- 
theless, they  present,,  in  their  entirety,  so  many  peculiarities  that  names 
which  they  received  earlier  are  still  used  in  describing  them. 

In  the  accompanying  illustration  let  us  first  follow  the  cortex  from 
below  upward. 

That  part  of  the  hippocampal  lobe  upon  which  the  part  that  is  rolled 
up  rests  is  designated  as  the  subiculum  cornus  Ammonis. 

It  is  covered  by  an  uncommonly  well  developed  layer  of  tangential 
fibers,  the  reticulated  arrangement  of  which  is  apparent  even  in  the  fresh 
brain.  Many  of  these  fibers,  traversing  the  entire  thickness  of  the  cortex, 
appear  to  extend  into  the  medullary  layer  of  the  convolution.  At  the  place 
where  the  inrolling  begins  the  layer  of  tangential  fibers  becomes  thinner, 
but  it  accompanies  the  entire  gyrus  hippocampi  farther  and  lies,  as  a  glance 
at  the  figure  must  show,  directly  upon  the  cortex  of  the  gyrus  dentatus. 
This  also  possesses  a  layer  of  tangential  fibers.  In  man  it  is  difficult 
to  separate  the  tangential  fibers  of  the  gyrus  hippocampi  from  those  of 
the  gyrus  dentatus;  they  form  together  a  single  layer.  The  dendrites 
of  the  cortical  cells  extend  into  this  layer  exactly  as  is  shown  in  Fig. 
152  for  the  rest  of  the  cortex  :  on  one  side,  the  dendrites  from  the 
cortex  of  the  dentatus;  on  the  other,  the  dendrites  from  the  cortex  of  the 
cornu  Ammonis.  A  second  large  layer  of  medullated  fibers  lies  beneath  the 
layer  of  tangential  fibers  in  the  region  of  the  gyrus  hippocampi.  This 
curved  plate  of  fibers,  the  lamina  medullaris  circumvoluta,  is  a  system  of 


COKTEX    OF    FOREBRAIX    AXD    MEDULLA    OF   HEMISPHEEES.  235 

association-fibers  which  arises  in  the  cornu  Ammonis  and  terminates  at  the 
place  where  this  is  surrounded  by  the  gyrus  dentatus. 

The  fibers  must  belong  to  the  cortex  itself,  and  not  simply  penetrate  thither, 
for  in  a  dog  in  which  a  single  gyrus  hippocampi  only  remained  of  the  entire  cerebral 
•cortex,  this  system  was  shown  to  be  entirely  preserved. 


Fig.  154. — Section  through  the  base  of  the  brain  and  the  gyrus  hippocampi 
lying  under  it.  (After  a  preparation  stained  with  haematoxylin-copper-lake.) 
The  plexus  chorioideus  is  drawn  somewhat  simpler  than  it  is  in  the  adult.  Notice 
that  it  separates  the  ventricle  from  the  cavity  of  the  skull,  and  the  manner  in 
which  it  is  done.  Tangentialfasern,  Tangential  fibers. 

The  lamina  medullaris  circumvoluta  lies  in  the  region  of  the  long 
dendrites,  which  the  cells  of  the  gyrus  hippocampi  give  off.  The  directing 
of  so  many  long  dendrites  outward  gives  to  this  stratum  a  slightly  striated 


236  ANATOMY    OF    THE    CENTRAL    NERVOUS    SYSTEM. 

appearance  on  section.  It  has  therefore  been  designated  as  the  stratum 
radiatum.  The  cells,  themselves,  in  the  hardened  preparations,  appear  to 
lie  in  large  cavities.  Thus,  their  long  curved  course  appears  as  a  clear  layer, 
and  has  received  the  name  of  stratum  lucidum.  Besides  their  dendrites,  they 
send  a  part  of  their  neuraxons  also  out  to  the  layer  of  tangential  fibers,  ex- 
actly as  in  the  rest  of  the  cortex.  The  greater  part  of  the  neuraxons,  how- 
ever, pass  ventrally,  and  these,  with  other  fibers,  then  form  a  true  medul- 
lary layer,  the  alveus,  which  lies  directly  underneath  the  ventricular  epi- 
thelium. The  small  space  between  the  stratum  lucidum  and  the  alveus 
is  filled  by  numerous  fibers  passing  into  the  cornu  Ammonis  and  by  fibers 
leaving  it.  It  contains  innumerable  fiber-branchings  and  a  number  of  very 
remarkable  association-cells,  which  we  have  only  recently  become  acquainted 
with  through  Ramon  y  Cajal.  They  are  adapted  in  consequence  of  their 
much-branched  neuraxon,  which  penetrates  into  the  cell-layer  of  the  stratum 
lucidum,  to  connect  well  together  the  pyramidal  cells  of  the  gyrus  hippo- 
campi (see  Fig.  9).  The  entire  layer  is  designated  as  the  stratum  oriens. 

All  investigations  on  the  cortex  of  the  cornu  Ammonis  show  that  there 
exists  here  an  abundance  of  cells  and  a  multiplicity  of  fiber-relations  which, 
so  far  as  is  known,  has  no  counterpart  in  all  the  remaining  cortex. 

If  what  is  typical  in  the  structure  of  the  cerebral  cortex  be  once  com- 
prehended, it  is  not  difficult  to  recognize  the  type  in  regions  where  it  is  less 
distinct.  The  bulbus  olfactorius,  for  example,  formerly  was  not  understood 
at  all.  If  Fig.  142  is  inverted  and  compared  with  Fig.  152,  the  similarity 
strikes  the  eye  at  once.  We  are  here  concerned  with  a  cortex  in  the  mo- 
lecular layer  of  which  the  olfactory-nerve  fibers  enter,  and  terminate  by 
splitting  up  into  an  arborization.  But  the  entire  cortex  is  more  condensed. 
The  entrance,  also,  of  the  olfactory-nerve  fibers  into  the  layer  of  tangential 
fibers  of  the  surface,  and  the  different  manner  in  which  the  dendrites  of  the 
cortical  pyramids  divide  and  terminate,  occasioned  by  the  former,  give  to 
the  whole  an  appearance  that  has  hitherto  rendered  difficult  of  perception 
the  fact  that  we  are  here  dealing  with  nothing  other  than  a  common  cortical 
formation. 

The  surface  of  the  cerebral  cortex  is  covered  in  man  (Weigert)  by  a 
dense  net-work  of  neuroglia,  from  which  numerous,  but  somewhat  widely 
separated,  prolongations  radiate  down  into  the  region  of  the  smaller  pyra- 
mids. Then  the  net-work  of  neuroglia  constantly  becomes  thinner,  and  in 
the  deepest  layers  of  the  cortex  it  is  almost  entirely  wanting.  Within  the 
radii  separate  fibrils  only  are  perceptible.  In  the  medullary  layer  there 
again  lies  a  relatively-dense  accumulation  of  neuroglia,  which  everywhere 
surrounds  the  medullated  fibers. 

If  the  nervous  elements  of  the  cerebrum  are  destroyed — e.g.,  in  paralyses — there 
appears  in  their  place  an  hypertrophy  of  neuroglia  which  is  characterized  not  only 


COETEX   OF   FOREBRAIX   ANTD    MEDULLA    OF   HEMISPHERES.  237 

by  its  appearance  in  an  abnormal  place,  but  also  by  the  thickness  of  its  fibers,  which 
by  far  exceed  the  otherwise  normal  fibers.  Only  in  extreme  age,  where — probably 
in  consequence  of  the  senile  cachexia — there  is  somewhat  more  neuroglia  in  the  cere- 
bral cortex,  do  such  fibers  occur.  Where  many  of  the  glia-platelets  cross,  there  arise 
the  astrocytes  and  "cells"  of  Deiter,  which  are  very  frequently  met  with,  therefore, 
in  paralyses. 

As  exact  a  knowledge  as  is  possible  of  the  cerebral  cortex  is  justly  striven  for 
in  all  directions.  Psychiatry  can  boast  pleasing  results  which  have  come  from  studies 
in  this  field.  I  will  only  mention  the  discovery  of  Tuczeck,  who  demonstrated  that 
in  the  progressive  paralyses  of  the  insane  the  net-work  of  nerve-fibers  in  the  first 
layer  was  the  first  to  degenerate,  and  that  the  fibers  in  the  deeper  layers  then  suc- 
cessively disappear  as  far  as  into  the  fourth.  A  similar  process  has  later  been  proved 
for  other  psychoses,  and  more  recent  discoveries  have  shown  that  in  the  deeper  parts 
of  the  brain  also  a  degeneration  of  fine  fibers  occurs  in  paralyses.  This  is  here  and 
there  occasioned,  PS  the  course  of  its  spreading  allows  us  to  infer,  through  the  sec- 
ondary degeneration  of  fibers  interrupted  in  the  cortex. 

The  nerve-fibers  in  the  cerebral  cortex  become  medullated  only  very.  late. 
Medullation  occurs  in  the  ninth  month  of  fetal  life  first  of  all  in  the  superior 
parietal  lobule  and  in  the  posterior  central  gyms;  in  the  first  month  of  extra-uterine 
life  single  fibers  in  the  anterior  central  gyrus  are  added  to  these;  later,  in  the  sec- 
ond and  third  months,  the  process  begins  in  the  occipital  lobe  of  the  cortex.  It  is 
probable  that  these  events  stand  in  relation  to  the  time  at  which  man  begins  to 
store  up  impressions  in  the  separate  regions  of  the  brain;  that,  for  example,  with 
the  acquisition  of  visual  perception,  the  optical  centers  of  the  cortex  first  begin  their 
development. 

In  later  life  more  extended  regions  are  constantly  becoming  medullated  (see 
page  231). 

The  white  medulla  of  the  hemisphere  lies  beneath  the  cortex.  This 
homogeneous  white  substance,  revealed  to  the  naked  eye  by  a  section  through 
the  centrum  semiovale,  is  resolved  by  the  microscope  into  a  large  number 
of  fibers  crossing  one  another  in  various  directions,  but  the  separate  fibers 
are  traced  only  with  difficulty.  Let  us  endeavor,  so  far  as  at  present  possible, 
to  become  acquainted  with  these  fibers. 

If  sections  are  made  through  the  fresh  brain  of  a  newborn  child,  it 
will  be  seen  that  there  lies  almost  everywhere  beneath  the  cortex  a  peculiar 
grayish-red,  transparent  mass,  in  which  white  nerve-fibers  are  to  be  found 
at  one  small  spot  only:  beneath  the  upper  portion  of  the  posterior  central 
gyrus  and  in  its  neighborhood.  In  the  course  of  the  first  months  of  life 
other  nerve-tracts  become  medullated:  first  of  all  those  tracts  mostly  which 
pass  downward  from  the  cortex;  soon,  however,  tracts  also  that  connect  sepa- 
rate cortical  regions  with  one  another. 

The  latter,  the  fibres  proprice  of  the  cortex,  are  exceedingly  numerous  in 
the  adult  brain;  they  everywhere  extend  from  gyrus  to  gyrus,  connecting 
distant  gyri  and  those  adjacent  to  one  another.  They  also  connect  entire 
lobes.  Apparently  these  "association-fibers"  arise  only  in  consequence  of 
the  association  of  two  cortical  regions  in  a  common  action;  in  other  words, 


238  ANATOMY    OF   THE    CENTRAL    NERVOUS    SYSTEM. 

these  fibers  are  developed  as  distinct  medullated  tracts  from  the  indifferent 
mass  of  nerve-fibers  whenever  they  are  brought  into  use  more  frequently 
than  other  tracts.  These  association-fibers  lie  for  the  great  part  close  be- 
neath the  cortex,  another  part  in  the  medullary  layer  of  the  hemispheres. 
Such  a  system  is,  as  you  see,  thoroughly  adapted  to  bringing  all  parts  of  the 
brain  in  communication  with  one  another.  The  manifold  processes  of  asso- 
ciation in  thought,  in  motion,  and  in  sensation,  for  which  the  brain  serves, 
may  possibly  find  their  anatomical  basis  in  the  fibers. 

It  is  not  improbable  that  these  fibers  play  an  important  r6le  in  the  spreading  of 
the  epileptic  seizures.  It  is  possible,  in  animals,  to  call  forth,  first,  contractions  in 
the  muscles  by  irritating  the  region  of  the  cortex  with  which  they  are  respectively 
connected,  and,  second,  convulsions  of  the  entire  affected  side  by  increasing  the  irri- 
tation. The  sequence  of  these  convulsions  corresponds  to  the  arrangement  of  the 
affected  centers  in  the  cerebral  cortex.  As  this  impulse  spreads  a  neighboring  motor 


Fig.  155. — Schema  of  the  fibrse  propriee  of  the  cortex. 

center  is  never  skipped  over.  The  convulsions,  when  they  have  completely  spread 
over  one-half  of  the  body,  involve  the  other  half  under  certain  conditions  (intensity 
of  the  irritation,  disposition  of  the  animal  experimented  on).  Extirpation  of  the 
single  motor  centers  occasions  an  omission  of  the  groups  of  muscles  involved  from 
the  general  convulsive  seizure. 

It  is  not  necessary  that  the  cortical  point  from  which  such  a  convulsive  seizure 
starts  belong  directly  to  the  motor  region.  The  convulsions  thus  produced  have  the 
greatest  similarity  to  the  symptoms  of  partial  or  general  epilepsy  in  man.  Since 
the  writings  of  Huglilings  Jackson,  especially,  forms  of  epilepsy  have  been  recog- 
nized that  begin  with  contractions  or  convulsions  in  one  limb  and  at  times  spread 
over  the  other  limbs  or  the  entire  body.  In  the  latter  case  they  present  a  typical 
picture  of  an  epileptic  seizure.  Consciousness  almost  never  disappears  entirely  so 
long  as  the  attack  remains  partial.  After  the  attack  paralyses  sometimes  remain, 
which  are  mostly  localized  in  the  parts  first  attacked.  This  partial,  or  cortical, 
epilepsy  is  not  to  be  separated  from  the  classical  epilepsy.  The  latter  probably  rep- 
resents a  form  in  which  the  initial  symptoms  follow  one  another  in  more  rapid  suc- 
cession. 

It  is  not  necessary,  however,  that  the  spreading  of  an  impulse  from  one  point 


CORTEX    OF    FOREBRAIX    AND    MEDULLA    OF   HEMISPHERES. 


239 


of  the  cortex  to  another  or  over  the  entire  brain  occur  precisely  by  way  of  the  fibrae 
propriae.  Many  other  ways  are  presented,  as,  for  instance,  the  fine  net-work  of 
nerve-fibers  on  the  surface  of  the  cortex;  then,  too,  the  entire  cortex  may  be  in- 
fluenced simultaneously  by  a  variation  in  the  volume  of  blood  in  its  vessels. 

The  tracing  of  the  fibrae  propriae  between  two  neighboring  cortical 
regions  is  not  extremely  difficult  if  the  teasing  method  is  employed.  The 
demonstration  of  connections  between  regions  lying  farther  apart  from  one 
another  is  much  more  difficult  and  leads  very  easily  to  artefacts,  which  cor- 
respond in  part  to  the  actual  direction  of  the  fibers.  A  few  tracts  only  are- 
to  be  followed  with  some  degree  of  certainty.  Such  are  the  fasciculus  un- 
cinatus,  the  fasciculus  arcuatus,  the  fasciculus  longitudinalis  inferior,  the 
cingulum,  and  a  few  others. 


Fig.  156.— Diagram  of  the  course  of  the  long  association-pathways. 


The  fasciculus  uncinatus  arises  from  the  cortex  of  the  temporal  lobe, 
passes  forward  close  to  the  ventral  margin  of  the  insula,  and  becomes  lost  in 
the  most  ventral  regions  of  the  frontal  lobe  (Figs.  170  to  172).  The  fas- 
ciculus arcuatus  passes  along  over  the  dorsal  part  of  the  insula  from  the 
more  posterior  portion  of  the  temporal  lobe  to  the  cortex  of  the  parietal 
and  frontal  lobes.  Fibers  accompany  it  (doubtful)  which  arise  in  the  frontal 
lobe  and  terminate  in  the  cortex  of  the  occipital  lobe  (see  Figs.  169  to  172). 

The  cingulum  is  a  long  tract  that  runs  in  the  marginal  gyrus — the  gyrus 
fornicatus — from  the  cortex  of  the  cornu  Ammonis  to  the  most  ventral 
region  of  the  frontal  lobe,  and  perhaps  to  the  olfactory  lobe  also  (dog  and 


240  ANAT01IY    OF   THE    CENTRAL   NERVOUS    SYSTEM. 

rabbit).     It  probably  consists  (Beevor)  of  several  separate  parts,  and  does 
not  entirely  degenerate  after  section  (see  Figs.  169  to  172). 

The  fasciculus  longitudinalis  inferior,  a  very  large  tract  of  fibers,  con- 
nects the  temporal  lobe  with  the  occipital  lobe  (see  Figs.  186  to  188). 

Dejdrine,  who  has  studied  this  bundle  very  thoroughly  in  its  relations  to  many 
other  parts  of  the  fiber-systems  of  the  brain,  observed  that  it  was  degenerated  in  a 
case  of  pure  word-blindness.  This  fact  and  the  course  of  the  tract  make  it  very 
probable  that  essentially  it  serves  to  carry  optical  impressions  to  other  parts  of  the 
brain.  It  exists  in  other  Primates  also.  Flechsig  has  lately  felt  compelled,  as  a 
result  of  embryological  studies,  to  exclude  this  bundle  entirely  from  the  system  of 
association-pathways.  It  is  said  not  to  terminate  in  the  temporal  lobe,  but  to  curve 
up  near  the  apex  of  the  same,  into  the  thalamus;  so  that  it  would  consequently  be  a 
part  of  the  radiatio  occipito-thalamica. 

Sachs  justly  emphasizes  the  fact  that  the  temporal  lobe  is  really  con- 
nected with  all  the  remaining  parts  of  the  brain  by  means  of  long  tracts 
only.  There  is  localized  in  it,  as  the  researches  of  pathology  show,  the 
auditory  imagery  of  speech.  The  very  abundant  possibilities  of  communi- 
cation may  correspond  to  the  importance  which  such  auditory  factors  have 
in  human  thought. 

In  Fig.  156  the  long  association-pathways  above  mentioned  are  com- 
bined diagrammatically.  One  tract  only  is  not  included  there,  because  until 
recently  it  was  very  questionable  whether  or  not  it  represented  a  long  asso- 
ciation-pathway. It  is  the  fasciculus  fronto-occipitalis.  Arising  from  the 
medullary  covering  of  the  posterior  and  lateral  horns  of  the  ventricle,  its 
fibers  pass  forward  as  a  well-defined  bundle  external  to  the  lateral  ventricle. 
They  always  keep  close  beneath  the  corpus  callosum  and  on  the  dorsal  edge 
of  the  nucleus  caudatus  (see  Figs.  170  to  172). 

It  is  the  same  tract  that  I  designated  earlier  as  the  association-bundle  of  the 
caudate  nucleus  (Fig.  168).  Investigations  by  Dtjerine,  Rietz,  and  Muratow  have 
shown,  however,  that  we  are  here  really  concerned,  as  Forel  and  Onufrowicz  had 
conjectured,  with  an  association-bundle  between  the  medulla  of  the  occipital  lobe 
and  that  of  the  frontal  pole.  Consequently,  the  bundle  will  be  found  designated  as 
the  fasciculus  fronto-occipitalis  in  the  large  frontal  sections  through  the  entire  brain, 
to  be  shown  later.  Moreover,  the  smaller  part  only  of  this  tract  of  fibers  is,  like  all 
longer  association-bundles,  composed  of  fibers  of  very  great  length;  a  far  greater 
part  consists  of  fibers  that  connect  together  single  sections  of  its  long  course. 

It  is  perfectly  proper  to  designate  all  of  these  long  tracts  as  interlobular 
association-bundles,  and  to  distinguish  them  from  those  that  connect  with 
one  another  separate  points  within  this  or  that  lobe.  These  intralobular 
tracts  have  been  little  studied  hitherto.  They  are  best  known  for  the  occipi- 
tal lobe,  where  pathways  have  been  demonstrated  by  Sachs,  Wernicke,  Viault, 
and  others,  which  are  adapted  to  connect  with  one  another  various  regions 
and  layers  of  this  lobe  in  all  directions. 


THE    COMMISSURES.  241 

Besides  these  fibers,  which  connect  parts  of  the  same  hemisphere  with 
each  other,  there  are  also  fibers  that  connect  one  half  of  the  cerebrum  with 
the  other.  Almost  all  of  these  fibers  run  in  the  corpus  callosum  and  in  the 
anterior  commissure,  thus  passing  transversely  through  both  hemispheres 
from  one  to  the  other. 

Inasmuch  as  I  presuppose  that  the  macroscopic  relations  of  the  corpus 
callosum  are  known  to  you — at  least  its  general  form,  where  it  is  distinct 
from  the  other  brain-mass — little  remains  to  be  said  by  way  of  explanation 
of  the  accompanying  illustration  (Fig.  157). 

It  must  be  borne  in  mind  that  just  as  the  fibers  of  the  corpus  callosum 
are  seen  passing  transversely  from  side  to  side  in  this  section  (which  is  made 
about  through  the  chiasma),  so  they  are  to  be  seen  in  the  whole  region  of  the 
brain  over  the  lateral  ventricles. 


Fig.  157. — Frontal  section  through  the  forebrain.     Diagram  of  the  course 
of  the  corpus  callosum  and  the  commissura  anterior. 


From  the  frontal  lobe,  also,  the  corpus  callosum  receives  on  each  side 
a  large  afferent  bundle  that  grows  to  it  anteriorly  over  the  roof  of  the  lateral 
ventricle,  on  its  lateral  side.  The  fibers  of  the  corpus  callosum  from  the 
occipital  lobe  closely  surround  the  posterior  horn  like  a  cap.  Their  radia- 
tion is  known  as  the  forceps  major.  The  portion  of  the  corpus  callosum 
passing  into  the  temporal  lobe  on  the  lateral  side  of  the  inferior  horn  is 
called  the  forceps  minor.  The  inner  side  of  the  posterior  horn  and  that  of 
the  inferior  horn  are  covered  by  a  layer  of  white,  medullated  fibers,  the 
tapetum.  (Compare  the  sections  through  the  fibers  of  the  corpus  callosum 
which  are  shown  in  Figs.  169  to  174  and  185  to  188.) 

The  simple  methods  of  sectioning  formerly  employed  made  this  entire  layer 
originate  like  the  fibers  of  the  corpus  callosum,— made  it  appear,  in  a  measure,  as  the 


24:2  ANATOMY   OF   THE    CENTKAL    XEEVOUS    SYSTEM. 

most  mesial  radiation  of  the  fibers  of  the  forceps.  Lately,  however,  the  investiga- 
tions of  the  authors  cited  above,  in  connection  with  the  fasciculus  fronto-occipitalis, 
make  it  probable  that  the  tapetum  does  not  radiate  into  the  corpus  callosum;  rather 
that  it  is  the  most  posterior  radiation  of  that  long  association-tract.  The  radiation 
of  the  fasciculus  fronto-occipitalis  lies  directly  beneath  the  epithelium  of  the  ven- 
tricle, next  to  the  cavity,  and  only  outside  of  it  lie  the  posterior  radiations  of  the 
corpus  callosum. 

For  all  that,  it  appears  to  me  that  numerous  fibers  of  the  corpus  callosum  are 
mixed  with  these.  At  least,  the  relatively  small  medullated  bundles  that  form  the 
fasciculus  fronto-occipitalis  in  the  dog  do  not  cover  all  the  numerous  fibers  of  the 
tapetum.  The  fact  that  the  tapetum  has  been  observed  to  be  present  in  cases  where 
the  corpus  callosum  was  wanting,  and  the  fact  that  it  does  not  degenerate  after 
section  of  the  corpus  callosum,  appear  to  be  the  most  important  reasons  for  per- 
mitting it  to  be  separated  from  the  corpus  callosum. 

In  the  osmatic  mammals,  where  the  cornu  Ammonis  extends  upward  as  far  as 
the  under  surface  of  the  corpus  callosum,  it  is  recognized  more  clearly  than  in  man 
that  the  posterior  end  of  the  corpus  callosum  curves  forward  again.  In  this  man- 
ner it  forms  a  distinct  layer  of  fibers  dorsal  to  the  psalterium,  which,  in  sections,  is 
to  be  distinguished  from  the  fibers  arising  from  the  cornu  Ammonis  by  the  smaller 
diameter  of  its  fibers  only.  This  portion  of  the  corpus  callosum,  as  well  as  the  dorsal 
portion,  is  penetrated  by  the  bundles  of  the  fornix  longus  (Fig.  144). 

The  accompanying  illustration  (Fig.  158)  represents  the  fibers  of  the 
corpus  callosum  when  exposed  from  the  inner  surface  of  the  brain.  With 
its  help,  an  accurate  idea  may  be  easily  formed  of  the  radiation  of  the  corpus 
callosum. 

The  commissura  anterior  has  already  been  described  in  connection  with 
the  description  of  the  olfactory  apparatus.  In  man  it  passes  as  a  large 
bundle  of  fibers,  close  to  the  floor  of  the  ventricle,  in  front  of  the  pillars  of 
the  fornix.  It  cannot  be  followed  in  a  transverse  section  in  the  manner 
intimated  in  the  semidiagrammatic  figure  here.  On  each  side  its  fiber-mass, 
while  it  passes  through  the  corpus  striatum,  curves  much  more,  downward 
and  backward,  in  a  semicircle  and  is  lost  in  the  most  posterior  portion  of  the 
medulla  of  the  lobus  temporalis.  In  Fig.  127  this  curved  portion  is  cut  on 
both  the  right  and  left  sides  below  and  external  to  the  nucleus  lentiformis. 

The  greatest  part  of  the  anterior  commissure  in  man  contains  only  fibers 
that  can  be  traced  backward  until  in  the  region  lateral  to  the  cornu  Ammonis 
(compare  Fig.  154).  A  small  bundle  only  of  the  commissure  of  the  olfactory 
lobe  is  shown, — it  is  seen  passing  downward  in  Fig.  157. 

Numerous  fibers  arise  from  all  parts  of  the  cortex  of  the  forebrain,. 
which  connect  the  forebrain  with  the  deeper-lying  parts  of  the  central  nerv- 
ous system.  A  great  many  pass  into  the  interbrain;  others  may  be  traced  as 
far  as  the  gray  masses  of  the  midbrain  and  as  far  as  into  the  nerve-nuclei 
of  the  pons,  in  which  they  appear  soon  to  terminate.  Some  of  them  pass 
down  through  the  internal  capsule,  the  crus  cerebri,  the  pons  and  the 


THE    COMMISSURES. 


243 


medulla  oblongata,  into  the.  spinal  cord,  where  the  fibers  enter  the  gray 
substance  at  various  levels. 

Taken  together,  these  fibers  passing  downward  from  the  cortex  are 
designated  as  the  corona  radiata.  You  will  not  form  a  wrong  idea  of  this 
if  the  thalamus  is  imagined  as  placed  free  under  the  overarching  dome  of 
the  cerebral  cortex,  and  it  is  then  assumed  that  nerve-fibers  pass  to  it  from 
all  parts  of  the  cortex.  Tracts  of  fibers  enter  it  from  the  cortex  of  the 
frontal,  parietal,  temporal,  and  occipital  lobes — perhaps  tracts  of  fibers  from 
the  cortex  at  the  entrance  to  the  fossa  Sylvii  and  from  the  cornu  Ammonis 


CeH 


Coa 


Tlio 


Fli 


Fig.  158. — Posterior  portion  of  the  right  hemisphere  seen  from  the  inner 
surface.  By  teasing  out  with  forceps,  the  radiation  of  fibers  from  the  posterior 
end  of  the  corpus  callosum  (Splcnium,  Ccl*)  is  shown.  The  mass  under  the 
corpus  callosum  is  the  thalamus  options  (Tho).  On  the  wall  of  the  ventricle 
surrounding  it,  the  tapetum  (Tap).  A  part  of  the  fasciculus  longitudinalis  in- 
ferior (Fli)  is  also  to  be  seen  in  the  illustration.  The  thalamus  has  under  it  the 
pes  pedunculi  (B).  The  other  letters  refer  to  structures  that  will  be  mentioned 
in  the  text  later  on:  Rdf,  Vicq  d'Azyr's  bundle;  Raf,  Fornix;  Cca,  Corpus 
candicans;  //',  Nervus  opticus;  Fcp,  Forceps. 


244  ANATOMY    OF   THE    CENTEAL   NEBVOUS    SYSTEM. 

also  (the  latter  running  in  the  fornix).  Others  of  the  tracts  of  the  corona 
radiata,  however,  do  not  go  to  the  thalamus,  but  pass  on  farther  downward, 
in  front  of,  to  the  outside  of,  and  back  of  it,  to  terminate  in  centers  that 
lie  deeper. 

The  corona  radiata  is  therefore  composed  of  fibers  that  go  to  the  thala- 
mus  and  of  fibers  that  go  to  deeper  lying  parts. 

1.  Fibers  pass  to  the  thalamus  from  almost  the  entire  surface  of  the 
cortex,  and  by  no  means  so  few  bundles  as  the  diagram  before  you  would 
indicate.  These  fibers  unite,  in  part,  close  to  the  thalamus  to  form  thicker 
bundles,  which  are  called  the  pedicles  of  the  thalamus. 

MonaTcow  has  been  able  to  show,  by  means  of  numerous  cases  of  second- 
ary degeneration,  that  a  very  definite  cortical  zone  sends  its  fibers  to  each 
of  the  thalamic  nuclei.  We  shall  have  occasion  to  consider  these  in  more 
detail  later  on.  At  present  we  will  mention  only  some  of  the  most  important 


Fig.  159. — Diagram  of  the  fibers  of  the  corona  radiata,  especially  the  fibers  to  the 
thalamus.     U.  8.,  Inferior  pedicle;    Sehhiigel,  Thalamus. 


tracts  of  this  group,  known  as  the  tractus  cortico-thalamici.  First,  there  is 
the  cortical  tract  of  the  fillet.  It  arises  from  the  region  posterior  to  the 
anterior  central  gyrus  and  terminates  in  the  most  ventral  thalamic  nuclei. 
The  fibers  of  the  fillet  also  pass  thither  from  the  spinal  cord  and  medulla 
oblongata.  For  this  reason,  we  may  regard  the  tract  mentioned  as  the  con- 
tinuation of  a  considerable  part  of  the  sensory  radiation  to  the  cortex.  In 
the  posterior  region  of  the  thalamus  there  lies  a  part  of  the  primary  termina- 
tions of  the  optic  nerve.  The  afferent  tracts  from  the  cortex  to  these  are 
also  well  known.  They  pass  forward,  after  leaving  the  medulla  of  the 
occipital  lobe,  in  an  almost  horizontal  direction,  and  end  in  the  groups  of 
ganglia  of  the  posterior  region  of  the  thalamus.  In  Fig.  160  this  "optic 


THE    COMMISSUEES.  245 

radiation"  is  reproduced  from  a  horizontal  section  through  the  brain  of  a 
child  9  weeks  old. 

In  man  its  destruction  leads  to  homonymous  hemianopsia  (see  below).  In  ani- 
mals it  does  not  appear  to  be  of  so  great  importance,  for  the  occipital  cortex  may  be 
destroyed  on  both  sides  without  producing  permanent  actual  blindness.  The  real 
centers  for  the  sense  of  sight,  consequently,  lie  deeper.  Sight  may  be  retained  if 
these  alone  are  preserved;  it  is  impaired,  however,  when  the  connection  between 
these  centers  and  the  cortex  is  destroyed.  This  connection,  probably  serving  for 
psychical  processes,  is  most  important  in  man;  apparently  of  lesser  importance  in 
the  other  mammals,  it  is  wanting  entirely  in  lower  animals, — e.g.,  the  fish.  These, 
at  least  the  Teleostei,  see  without  possessing,  in  general,  anything  more  than  a  thin 
epithelial  vesicle  in  place  of  a  cerebrum. 

2.  Cortical  tracts  extend  into  the  midbrain,  partly  from  the  occipital 
lobe  by  way  of  the  above-mentioned  optic  radiation,  partly  from  the  tem- 
poral lobe  to  the  terminations  of  the  secondary  radiation  of  the  auditory 
nerve.     The  fibers  arising  from  the  end-nuclei  of  the  acusticus  extend  up- 
ward as  far  as  into  the  ganglia  of  the  midbrain.    There  they  soon  end,  but 
the  cortical  tracts  begin  at  the  place  where  they  terminate. 

3.  In  the  region  ventral  to  the  thalamus  a  tract  is  soon  lost  to  further 
observation  which  Fkchsig  has  named  the  tegmental  radiation.     From  the 
cortex  of  the  superior  parietal  lobule  (and  from  the  posterior  central  gyrus?), 
perhaps  from  cortical  regions,  also,  lying  still  farther  posterior,  its  fibers 
extend  into  the  internal  capsule  and  pass,  in  part,  below  the  thalamus, 
toward  the  spinal  cord;    in  part,  they  sink  into  the  lenticular  nucleus. 
They  pass  through  the  two  inner  divisions  of  the  lenticular  nucleus,  then 
unite  again  close  to  the  base  of  the  brain  to  form  a  more  compact  bundle, 
the  course  of  which  we  shall  become  familiar  with  later.    These  fibers  are 
the  first  to  become  medullated  in  the  cerebrum.     They  alone  are  to  be 
recognized  in  fetuses  of  the  eighth  to  ninth  month  as  thin,  white  tracts 
in  the  internal  capsule,  which  at  this  time  appears  gray  (Fig.  2). 

But  this  is  not  the  end  of  the  cortical  radiation.  Its  most  caudal  por- 
tions pass  into  the  pons,  the  medulla  oblongata,  and  the  spinal  cord. 

4.  The  cortical  tracts  to  the  pons,  tractus  corticis  ad  pontem,  are  divided, 
after  Flechsig,  into  the  frontal  system  from  the  frontal  lobe,  and  the  pos- 
terior, from  the  occipital  and  temporal  lobes.     The  fibers  end  in  the  pons 
in  large  ganglia,  from  which  originate  the  peduncles  of  the  cerebellum. 

5.  The  speech-tract,  the  tractus  cortico-bulbaris,  runs  to  the  nuclei,  in 
the  oblongata,  of  the  nerves  that  are  necessary  for  speech.    Its  origin  in  the 
cortex  of  the  inferior  frontal  gyrus,  its  course  through  the  medullary  layer 
external  to  the  tail  of  the  nucleus  caudatus  and  its  termination  in  the  above- 
mentioned  nuclei,  all  have  been  inferred  from  clinical  cases  that  have  been 
carefully  observed  and  verified  by  autopsies.    It  has  not  as  yet  been  demon- 


246  ANATOMY    OF    THE    CENTBAL   NEKVOUS    SYSTEM. 

strated  by  actual  anatomical  investigation.  The  speech-tract,  where  it  passes 
over  the  anterior  part  of  the  nucleus  lentiformis,  lies  very  near  to  the 
central  liypoglossal  tract.  In  it  lie,,  also,  most  probably,  the  small  tracts  that 
serve  to  bring  about  voluntary  movement  of  the  vocal  cords. 

6.  The  cortical  tracts  to  the  spinal  cord,  tractus  cortico-spinales,  arise 
from  the  cortex  of  the  central  gyri  and  the  paracentral  lobule  only.  They 
pass  down  into  the  lateral  and  anterior  columns  of  the  cord,  and  are  known 
as  the  pyramidal  tracts. 

There  doubtless  still  exists  a  large  number  of  other  systems  belonging 
to  the  corona  radiata. 

Brains  with  recent  apoplectic  lesions  form  excellent  material  for  in- 
vestigations that  are  directed  toward  the  finding  of  such  systems.  About 
three  weeks  after  the  appearance  of  such  an  attack,  upon  application  of 
Marchi's  osmium  method,  tracts  of  fibers  will  always  be  found  undergoing 
a  descending  degeneration,  which  extends  far  down  from  the  point  of  lesion 
(Hoche). 

The  brains  of  children  of  the  first  years  of  life  are  also  very  instructive. 
The  fibers  become  medullated  at  different  periods,  and,  so  far  as  is  known 
at  present,  the  entire  corona  radiata  has  become  medullated  by  the  end  of 
the  second  year. 

As  a  result  of  such  investigations,  Fleclisig  has  now  advanced  the  very 
interesting  conclusion  that  the  fibers  of  the  corona  radiata  pass  out  from  by 
no  means  all  parts  of  the  cerebral  cortex;  that,  on  the  other  hand,  there  are 
regions  which  form  their  white  medullary  substance  essentially  of  asso- 
ciation-tracts. Accordingly,  the  mantle  region  may  ~be  divided  into  two  grand 
divisions  which  differ  as  to  structure.  The  first  contains,  besides  the  bundles 
of  the  corona  radiata  mentioned  above — among  which  the  tractus  cortico- 
thalamici  are  the  largest — association-fibers  and  fibers  of  the  corpus  cal- 
losum  in  abundance.  From  here  originate  the  sensory  systems  of  fibers,  and 
those  fibers  also  for  the  innervation  of  the  muscles  and  organs  of  speech. 
Fleclisig  calls  the  entire  region  the  sensory  centers.  It  includes  the  optic  cen- 
ter in  the  area  of  the  cuneus,  the  auditory  center  in  the  most  posterior  part  of 
the  first  temporal  gyms,  the  olfactory  center  in  the  gyrus  hippocampi  and  the 
ventral  part  of  the  frontal  lobe,  and,  finally,  that  large  field  which  includes 
the  posterior  portions  of  all  the  frontal  gyri  and  the  central  gyri,  the  same 
cortical  area  from  which  proceed  the  tractus  cortico-spinales  and  the  cortical 
pathway  to  the  termination'of  the  fillet.  All  of  the  fibers  belonging  to  these 
areas  become  medullated  earlier  than  those  parts  of  the  cortex  which,  in 
general,  contain  association-fibers  only.  Fleclisig  calls  these  association- 
centers.  They  include  four  large  regions:  the  anterior  portion  of  the  frontal 
lobe,  the  greater  part  of  the  temporal  lobe,  the  posterior  portion  of  the 
parietal  lobe,  and  the  insula  Eeilii.  Numerous  association  systems  connect 


THE    COMMISSURES.  247 

these  parts  with  two,  and  even  more,  neighboring  sensory  centers.  The 
speech-centers  appear,  as  a  whole,  to  lie  in  the  common  boundary  region  of 
the  sensory  and  association  centers. 

One  sees  that  even  the  short  description,  which  the  author  was  able  to 
give  here,  of  the  tracts  running  in  the  white  medullary  substance  shows  this 
to  be  a  very  complicated  structure.  In  fact,  sections  made  at  any  place 
whatsoever,  never,  or  almost  never,  show  one  of  the  systems  alone;  at  least, 
decussating  fibers  are  almost  always  present,  originating  from  the  associa- 
tion-bundles, or  from  the  corpus  callosum  also,  or  from  the  other  systems  of 
commissures.  Perhaps  the  collaterals,  the  exit  of  which  from  the  fibers  of 
the  corona  radiata  is  easily  demonstrable  in  the  mouse  by  means  of  the 
Golgi  method,  here  play  an  important  role  in  complicating  matters.  How- 
ever, one  recognizes  even  now  the  cardinal  feature  of  brain-structure  when 
one  sees  that  from  particular  cortical  areas  definite  fasciculi' pass  to  definite 
termini. 

Numerous  investigators  have  turned  their  attention  to  the  histology  of  the 
cerebral  cortex  and  the  finer  anatomical  relations  of  its  structure.  Hitherto  the  more 
it  was  investigated,  the  more  difficult  the  solution  of  the  problem  appeared  to  be. 
New  and  more  complicated  relations  were  constantly  becoming  known.  Baillarger, 
Sevan  Lewis,  Clarke,  Meynert,  Golgi,  Bellonci,  S.  Ramon  y  Cajal,  Kolliker,  and  many 
others  have  attempted  to  throw  light  upon  the  most  important  points.  The  cortex 
of  the  eornu  Ammonis  was  specially  investigated  by  Meynert,  Kolliker,  Henle,  Duval, 
Schaffer,  Golgi,  Sola,  and  Ramdn  y  Cajal.  Much  was  learned  concerning  the  sys- 
tem of  fibers  in  the  white  matter  of  the  hemisphere  by  F.  Arnold,  Reil,  and  Bur- 
dach,  even  by  means  of  the  teasing  method,  while  the  microscopic  investigations  by 
Meynert,  Sachs,  Brissaud,  and  Dejerine,  more  particularly  the  embryological  studies 
of  Flechsig,  and  the  numerous  experimental  researches  of  Gudden,  Lowenthal,  Mona- 
kow,  and  others,  have  advanced  our  knowledge  of  the  subject  wonderfully.  The 
advantages  that  have  accrued  to  the  study  of  the  anatomy  of  this  portion  of  the 
brain  from  investigations  on  pathological  brains  are  not  to  be  undervalued.  Wernicke, 
Charcot,  Fere,  Pitres,  Friedmann,  Sioli,  Monakoic,  Richter,  Zacher,  Dejerine  and 
others  have  made  such  investigations. 


CHAPTER    XVI. 

THE  CAPSTTLA  INTEBXA,  THE  CORPUS  STRIATUM,  AND  THE  GANGLIA 
OF  THE  INTERBRAIN. 

ON  their  way  downward  the  fibers  of  the  corona  radiata  enter  into  im- 
portant relations  with  the  corpus  striatum  and  the  thalamus  options.  They 
converge  accordingly  and  so  arrive  in  the  region  outside  of  the  thalamus. 


Fig.  160.— Horizontal  section  through  the  brain,  trending  downward  some- 
what toward  the  sides.  Bcilken,  Corpus  callosum.  Options  Strahlung,  Optic 
radiation. 


In  order  to  pass  thither  the  fibers  from  the  anterior  parts  of  the  brain  must 
penetrate  the  corpus  striatum.  This  will  be  made  clear  by  the  accompany- 
ing section,  made  horizontally  through  the  cerebrum. 

This  section  is  made  about  a  finger's  breadth,  below  the  section  shown 

(248) 


CAPSULA    INTERNA,    CORPUS    STRIATUM,    IXTERBRAIX-GANGLIA.        249 

in  Fig.  124.  You  must  understand  that  the  two  hemispheres  are  in  part  re- 
moved, and  bear  in  mind  that  their  coronal  fibers  passed  downward  from 
above  into  the  knee-shaped,  white  line  of  the  internal  capsule.  The  portions 
of  the  capsule  formed  by  fibers  coming  from  the  frontal  and  occipital  lobes 
lie  in  part  in  the  plane  of  the  section.  A  few  words  now  in  explanation  of 
this  section. 

The  frontal,  occipital,  and  temporal  lobes  are  recognized  immediately. 
The  temporal  lobe  lies  over  the  island  of  Eeil,  and  thus  partly  conceals  it. 
As  in  Fig.  125,  you  see  the  corpus  callosum  in  front  cut  transversely,  and 
adjoining  it  the  septum  pellucidum,  at  the  posterior  end  of  which  the  pillars 
of  the  fornix  ascend. 

Anteriorly,  external  to  the  septum,  lies  the  head  of  the  nucleus  cau- 
datus,  which  is  cut  into  in  this  section.  Its  tail,  which  was  seen  passing 


Fig.  161. — Nucleus  caudatus  exposed  along  its  entire  length  (diagram- 
matic). Ammonshorn,  Cornu  Ammonis.  Riechlappen,  Olfactory  lobe.  Ventrikel, 
Ventricle. 


along  the  side  of  the  thalamus  in  Fig.  125,  is  not  visible.  It  is  contained  in 
the  part  of  the  brain  removed.  Only  a  small  portion  of  it  is  still  to  be 
seen,  posteriorly  and  externally,  near  to  the  cornu  Ammonis.  The  above 
sketch,  which  represents  a  nucleus  caudatus  dissected  out,  shows  how  this 
condition  is  brought  about. 

The  tail  of  the  nucleus  caudatus  -bends  around  the  brain-stem  in  a 
gentle  curve,  and  is  to  be  traced  almost  to  the  apex  of  the  inferior  horn  of 
the  lateral  ventricle.  The  entire  nucleus  must  consequently  be  cut  twice 
in  every  horizontal  section  made  through  the  deeper  planes  of  the  brain. 
This  is  shown  by  the  line  a  &  in  Fig.  161. 

Thick  tracts  of  fibers  are  seen  external  to  the  head  of  the  nucleus  cau- 
datus. They  come  from  the  cortex  of  the  frontal  lobe,  and  contain  the 


250  AXAT01IY    OF    THE    CENTRAL    NERVOUS    SYSTEM. 

corresponding  fibers  of  the  corona  radiata  passing  to  the  thalamus,  and  the 
frontal  fibers  passing  to  the  pons. 

In  order  to  pass  into  the  thalamus  and  the  pons,  this  mass  of  fibers  must 
cut  through  the  ganglion  of  the  corpus  striatum,  which  lies  in  the  way 
(Fig.  160).  The  part  which  lies  nearer  the  median  line  is  the  aforesaid 
nucleus  caudatus;  the  part  that  comes  to  lie  more  external  is  the  nucleus 
lentiformis.  Nevertheless,  they  are  not  absolutely  separated  from  one  an- 
other by  the  fibers  from  the  frontal  lobes;  numerous  connecting  fibers  pass 
between  them.  The  above-mentioned  fibers  of  the  corona  radiata  to  the 
thalamus,  the  fibers  from  the  frontal  lobe  to  the  pons,  the  bundles  between 
the  head  of  the  nucleus  caudatus  and  the  nucleus  lentiformis,  and,  finally, 
other  fibers  from  the  nucleus  caudatus  to  the  thalamus  and  to  the  nucleus 
lentiformis,  all  of  these  fibers  together  constitute  the  white,  fiber-mass  of 
the  capsula  interna,  met  with  in  the  horizontal  section  shown  in  Fig.  160. 

The  frontal  section. reproduced  in  Fig.  162  is  intended  to  complete  the 
idea  of  these  relations  shown  in  the  horizontal  section.  Situated  very  far 
forward,  it  strikes,  principally,  the  ganglia  of  the  corpus  striatum,  and 
likewise  distinctly  shows  the  fibers  of  the  capsula  interna  separating  them. 

The  form  and  location  of  the  nucleus  caudatus  will  probably  be  clear 
to  you  now;  but  it  will  be  more  difficult  to  form  an  idea  of  the  peculiar, 
wedge-shaped  figure  of  the  nucleus  lentiformis.  A  study  of  the  horizontal 
section  and  of  the  frontal  section  (Fig.  162)  will  be  of  benefit  in  this  con- 
nection. Internally,  two  other,  somewhat  lighter-gray,  ganglionic  masses 
are  associated  with  this  ganglion,  which  are  intimately  attached  to  it  by 
fibers.  We  commonly  speak,  therefore,  of  a  threefold  division  of  the  lenticu- 
lar nucleus,  whereas  the  broad,  darker,  outer  division  alone,  the  putamen, 
probably  is  morphologically  equivalent  to  the  nucleus  caudatus.  This 
nucleus  caudatus  sends  its  fibers,  as  was  mentioned  above,  through  the  an- 
terior limb,  or  segment,  of  the  internal  capsule  to  the  two  inner  divisions  of 
the  lenticular  nucleus,  and  on  through  them  farther  downward.  The 
fibers  of  the  putamen  run  an  exactly  similar  course. 

External  to  the  corpus  striatum  lies  the  cortex  of  the  island  of  Eeil. 
In  the  narrow  strip  of  white  substance  which  lies  between  the  cortex  and 
the  ganglion,  the  capsula  externa,  there  is  situated  an  accumulation  of 
ganglionic  cells,  known  as  the  claustrum.  Anatomically,  this  is  somewhat 
different  from  the  neighboring  cortex,  and  it  extends  ventrally  as  far  as  into 
the  olfactory  field. 

Behind  the  nucleus  caudatus,  the  horizontal  section  shown  in  Fig.  160 
passes  through  the  thalamus,  the  interbrain.  In  front  of  this  the  pillars  of 
the  fornix  ascend  from  below.  The  commissura  media,  a  thin  band  of  gray 
matter,  extends  from  one  thalamus  to  the  other.  External  to  the  thalamus 
lies  the  posterior  limb  of  the  internal  capsule.  The  point  where  both  limbs 


CAPSULA    INTERXA,    CORPUS    STRIATUM,    INTERBRAIN-GANGLIA.        251 

meet  has  been  named  the  genu  (knee)  of  the  internal  capsule.  Impress  this 
peculiar  angular  form  of  the  capsula  interna  well  upon  your  memory.  The 
relation  of  the  separate  parts  of  the  corona  radiata  to  the  two  limbs,  or 
.segments,  is  probably  approximately  constant,  and  therefore  exceedingly  im- 
portant clinically.  In  the  posterior  limb,  for  the  most  part  near  the  genu, 
lie  the  fibers  running  from  the  motor  zone  to  the  extremities  (pyramidal 
tract).  Just  in  front  of  them  are  the  tracts  which  stand  in  relation  with 


Fig.  162. — Frontal  section  through  the  forebrain,  close  behind 
the  pillars  of  the  fornix. 


the  nuclei  of  the  facialis  and  hypoglossus,  and  which  arise  from  the  lower 
end  of  the  anterior  central  convolution. 

Behind  the  pyramidal  tract  the  tracts  designated  as  the  tegmental 
radiation  are  met  with  in  about  the  last  third  of  the  posterior  limb,  or  some- 
what more  anteriorly.  Adjoining  these  posteriorly  lies  the  tract  from  the 
occipital  lobe  to  the  origin  of  the  opticus.  According  to  clinical  facts,  there 
must  also  be  fibers  in  this  region  which  pass  from  the  cortex  of  the  temporal 
lobe  to  the  nucleus  of  the  acusticus,  and  also  fibers  which  stand  in  some 
relation  to  the  sense  of  smell.  Thus  there  meet,  in  the  posterior  third  of  the 


252 


ANATOMY    OF    THE    CENTRAL   NERVOUS    SYSTEM. 


posterior  limb  of  the  internal  capsule,  all  the  sensory  fibers  and  the  fibers 
connected  with  the  nerves  of  special  sense.  Besides  these,  moreover,  there 
are  here  found  coronal  fibers  to  the  thalamus  from  the  cortex  of  the  tem- 
poral and  occipital  lobes,  and  the  temporo-occipital  tract  to  the  pons.  The 
following  figure  shows  diagrammatically  the  relative  positions  of  the  sepa- 
rate tracts  composing  the  internal  capsule. 

All  of  these  fiber-masses,  therefore,  converge  from  the  cortex  toward  the  region 
lying  lateral  to  the  thalamus.  A  part  of  them  enters  the  thalamus  (corona  radiata 
of  the  thalamus) ;  another  part — and  that  the  larger — passes  under  the  thalamus, 
where  it  ends  in  ganglia  or  passes  on  farther  down  to  the  spinal  cord.  Lesions  that  lie 
in  the  centrum  semiovale  must,  therefore,  involve  part  of  the  fibers  of  the  corona 


Fig.  163. — Diagram  of  the  internal  capsule,  in  which  the  location  of  most 
of  the  tracts  of  fibers  which  compose  it  is  indicated  by  their  respective  names. 
Extremitaten  mot.  Balm,  Motor  tract  to  the  extremities.  Fasern  aus  Nucleus 
Caudatus,  Fibers  from  nucleus  caudatus.  Fasern  aus  N.  Lentiformis,  Fibers  from 
nucleus  lentiformis.  Frontale  Briickenbahn,  Frontal  cortical  tract  to  the  pons. 
Opticusfasern,  Optic  fibers.  Sensorische  Fasern,  Sensory  fibers.  Stabkranz  des 
Thalamus,  Corona  radiata  of  the  thalamus.  Stabkranz  zum  Thalamus,  Coronal 
fibers  to  the  thalamus.  Temporo-occipitale  Briickenbahn,  Temporo-occipital  cor- 
tical tract  to  the  pons. 


radiata.  But  by  no  means  always  do  they  produce  symptoms  which  lead  us  to 
suspect  an  interruption  in  the  conducting  pathway  from  the  cortex  to  the  periphery. 
This  is  probably  on  account  of  the  fact  that  the  coarser  lesion-symptoms  which  may 
be  detected  by  our  present  means  of  diagnosis  arise  only  whenever  the  entire  tract 
involved  is  destroyed.  It  appears  that  small  remnants  are  sufficient  to  conduct 
voluntary  impulses  from  the  cortex  to  the  deeper  parts,  or  to  convey  sensory  im- 
pressions from  the  periphery  to  the  cortex. 

Lesions,  in  particular,  that  do  not  lie  in   the  medullary  substance  under  the 


CAPSULA    IXTERXA,    CORPUS    STKIATUM,    IXTERBRAIX-GAXGLIA.        253 

central  convolutions — that  is  to  say,  lesions  which  involve  the  cortical  tracts  to  the 
pons  and  the  tegmental  radiation — often  fail  to  give  rise  to  symptoms.  Focal  lesions, 
on  the  other  hand,  that  involve  the  pyramidal  tract  produce  paralysis  of  the  opposite 
half  of  the  body.  Disease  of  the  medullary  substance  under  the  cortex  of  the  in- 
ferior frontal  convolution  often  leads  to  aphasia.  Moreover,  cases  are  known  which 
make  it  extremely  probable  that  interruption  of  the  tegmental  radiation  may  lead  to 
a  unilateral  loss  of  sensibility.  Two  cases  recently  observed  by  the  author  show  that 
the  pains  which  appear  after  apoplexies  may  at  times  be  explained  through  the  prox- 
imity of  the  lesion  and  the  tegmental  radiation. 

It  appears  fairly-well  established  that  diseases  which  involve  the  region  poste- 
rior to  the  knee  of  the  internal  capsule — that  is,  diseases  which  make  the  fibers 
running  in  this  region  incapable  of  conduction — suspend  the  motility  of  the  entire 
opposite  half  of  the  body;  that  lesions  situated  in  the  terminal  two-thirds  of  the 
posterior  limb  destroy  the  sensibility  of  the  opposite  half  of  the  body,  or  at  least 
diminish  it  very  much.  In  most  cases  the  sense  of  sight  suffers  also,  and  probably 
hearing  at  times.  The  disturbance  of  sight  appears  in  the  form  of  hemiopia. 


Cortical  centers  for  leg, 


Centrum  semiovale 


Capsula  interna 


Fig.  164. 


If  you  bear  in  mind  what  has  been  repeatedly  stated:  that  all  the  fibers  con- 
verge from  the  cortex  toward  the  internal  capsule,  it  will  be  easily  understood  that 
small  lesions  in  the  internal  capsule  may  produce  the  same  symptoms  as  larger  ones 
in  the  centrum  semiovale,  or  still  more  extensive  lesions  in  the  cortex.  In  the  internal 
capsule  fibers  lie  close  together  which  higher  up  are  spread  out  over  a  greater  space. 
For  example,  a  very  extensive  cortical  territory  (one  including  both  central  con- 
volutions and  the  parts  of  the  frontal  and  parietal  convolutions  closely  bordering  on 
them)  must  be  destroyed  if  complete  crossed  hemiplegia  is  to  be  produced.  A  smaller 
lesion  in  the  medullary  substance  of  the  centrum  semiovale  under  the  central  gyri 
might  have  the  same  effect.  In  the  internal  capsule,  on  the  other  hand,  the  destruc- 
tion of  a  small  portion  alone  of  the  posterior  limb  suffices  to  call  forth  the  combina- 
tion of  symptoms.  In  cases  of  hemiplegia,  therefore,  we  will  always  think,  first  of 
all,  of  lesions  which  are  in  the  neighborhood  of  fhe  internal  capsule  or  are  situated 
in  it,  if  additional  symptoms  do  not  point  directly  to  other  regions  of  the  brain. 


254  ANATOMY    OF   THE    CENTEAL   NERVOUS    SYSTEM. 

Hemiplegias  from  cortical  lesions  are  very  rare.  Hemiplegias  that  proceed  from  the 
midbrain  or  from  deeper-lying  points  are  still  more  rare,  and  are  mostly  associated 
with  symptoms  involving  the  cranial  nerves,  which  indicate  the  seat  of  the  lesion. 

On  the  other  hand,  both  anatomical  considerations  and  clinical  experience  teach 
us  that  cerebral  affections  involving  single  parts  of  the  body — for  example,  a  hand — 
are  only  very  rarely  produced  by  lesions  in  the  internal  capsule.  This  is,  indeed, 
because  the  fibers  are  so  closely  crowded  together  there  that  a  lesion  can  hardly  in- 
volve separate  bundles  of  fibers  alone  without  involving  those  near  by.  Monoplegias 
and  monospasms  not  infrequently  arise  from  cortical  lesions,  however.  There  a 
lesion  may  even  be  of  relatively  large  size  before  it  involves  a  neighboring  center. 
The  accompanying  diagram  (Fig.  164)  will  serve  to  elucidate  what  has  been  said. 
It  shows  why  monoplegias  proceed  more  frequently  from  the  cortex  and  hemiplegias 
more  frequently  from  deeper-lying  parts  of  the  brain;  for  it  is  at  once  seen  that  a 
lesion  of  given  extent  located  in  the  cortex  may  easily  involve  one  center  alone, 
whereas  a  similar  lesion  situated  farther  below  will  involve  the  fibers  of  many  centers. 

It  has  not  as  yet  been  learned  what  symptoms  appear  when  fibers  of  association- 
bundles  alone  are  involved,  on  account  of  the  proximity  of  these  fibers  to  the  corona 
radiata. 

Probably  certain  forms  of  disturbances  of  speech,  reading,  and  hearing  belong  in 
this  category.  Furthermore,  little  is  known  concerning  the  symptoms  appearing  after 
a  loss  of  function  (Functibnsausfall)  of  the  corpus  callosum.  It  appears  that  under 
certain  conditions  it  may  be  entirely  destroyed  without  the  appearance  of  disturb- 
ances of  motility,  of  co-ordination,  of  sensibility,  of  the  reflexes,  of  the  special  senses, 
or  of  speech,  and  without  the  manifestation  of  any  considerable  disturbance  of  the 
intellect.  Uncertain  gait,  without  actual  vertigo  or  ataxia,  was  once  observed  in  a 
case  of  disease  of  the  corpus  callosum. 

The  fibers  of  the  corona  radiata  terminate,  in  great  part,  therefore,  in 
the  interbrain,  in  the  thalamus  options.  The  other  fibers  pass  on  farther 
downward  and  backward  in  the  internal  capsule.  They  thus  come  to  lie 
free,  for  the  most  part,  on  the  under  surface  of  the  brain,  behind  the  thala- 
mus. These  thick,  white  bundles  there  emerging  frdm  the  brain-mass  are 
designated  as  the  foot  of  the  cms  cerebri,  pes  pedunculi,  or  crusta  (Fig.  165, 
below  and  to  left). 

As  is  seen  in  the  accompanying  frontal  section,  this  free  part  of  the 
internal  capsule,  the  fibers  of  which  curve  caudad  as  the  crus  cerebri,  lies 
ventral  to  the  thalamus.  Into  this  foot,  the  pes  pedunculi  of  the  crus  cerebri, 
pass  the  bundles  of  the  frontal  tract  to  the  pons,  those  of  the  temporal  tract 
to  the  pons,  and  those  of  the  pyramidal  tract.  The  coronal  fibers  of  the 
opticus  and  the  tegmental  radiation  do  not  enter  the  pes.  Farther  caudad, 
in  the  region  of  the  corpora  quadrigemina,  the  nerve-fibers  which  come 
from  the  thalamus  and  from  other  brain-parts,  also  those  from  the  tegmentai 
radiation,  lie  dorsal  to  the  pes  in  a  position  corresponding  to  that  of  the 
thalamus.  The  fibers  from  the  forebrain,  the  interbrain,  and  the  midbrain 
are  there  divided  into  a  ventral  part,  the  foot,  pes,  or  crusta, — and  a  dorsal 
part,  the  tegmentum. 


CAPSTJLA   INTERXA,    CORPUS    STRIATUM,    IXTERBRAIN-GANGLIA.        255 

A  very  instructive  section  may  be  made  which  gives  an  idea  of  the  origin  of  the 
fibers  found  in  the  pes.  Take  a  fresh  brain  and  cut  into  the  crus  cerebri  perpen- 
dicularly until  the  substantia  nigra  is  met  with.  Then  turn  the  knife  and  cut 
horizontally  through  both  hemispheres  in  a  direction  obliquely  upward  and  forward. 
The  section  upon  which  is  based  the  illustration  shown  in  Fig.  258  is  made  in  a  similar 
manner.  For  the  passing  of  the  fibers  from  the  internal  capsule  into  the  pes,  see 
Fig.  175. 


Fasc.  occip.-front. 
Nucl.  caudat. 


Nucl.  lentif. 
Rad.  occip.-thal. 
(optic  tract; 

Rad.  temporo-thal. 
-Nucl.  caadatus 


Fig.  165. — Frontal  section  through  the  forebrain  and  interbrain  close  to  the  place 
where  the  fibers  of  the  capsula  interna  become  fibers  of  the  pes  pedunculi. 


The  tracts  from  the  cortex  form  the  chief  mass  of  the  pes.  Dorsally 
there  is  added  to  them  a  small  tract  which,  coming  from  the  corpus  striatum, 
terminates  in  a  ganglion  situated  dorsal  to  the  pes,  in  the  substantia  nigra. 
It  is  the  stratum  intermedium  pedunculi. 

We  will  now  turn  our  attention  to  the  corpus  striatum  and  the  fiber- 
systems  arising  from  it. 

This  large  ganglion,  situated  at  the  base  of  the  forebrain,  is  divided 
by  the  fibers  of  the  internal  capsule  arising  in  the  cortex  into  the  nucleus 


256  ANATOMY    OF    THE    CENTRAL    NERVOUS    SYSTEM. 

lentiforrnis,  located  laterally,  and  the  nucleus  caudatus,  which  lies  dorsally 
and  mesially.  The  nucleus  lentiformis  consists  of  an  outer  division,  the 
putamen,  and  two  or  more  inner  divisions,  the  globus  pallidus.  From  the 
putamen  and  from  the  nucleus  caudatus  arises  the  fiber-system  of  the  corpus 
striatum.  Moreover,  the  corpus  striatum  is  traversed  by  a  system  of  fibers 
originating  in  the  cortex:  the  tegmental  radiation. 

The  fiber-system  of  the  corpus  striatum  itself  connects  the  same  with 
the  ganglia  of  the  interbrain.  It  passes,  in  part,  in  the  anterior  limb  of  the 
internal  capsule,  in  part — so  far  as  it  comes  from  the  putamen — under  the 
internal  capsule  at  the  base  of  the  brain,  to  the  interbrain.  Thus  the  latter 
portion  of  fibers  must  surround  the  fibers  of  the  internal  capsule  at  the 


Fig.  166. — The  fiber-system  which  arises  from  the  nucleus  caudatus  and 
passes  to  the  ganglia  of  the  interbrain  and  midbrain  (Radiatio  strio-thalamica) . 
The  fiber-system  of  the  lenticular  nucleus  is  not  represented.  It  would  run  from 
the  observer  toward  the  thalamus. 


place  where  they  come  to  lie  free  at  the  base  of  the  brain  as  the  pes  pedun- 
culi.  This  part  is  designated  as  the  loop  of  the  lenticular  nucleus,  or  ansa 
lentiformis.  It  contains  essentially  the  fibers  from  the  putamen. 

We  are  here  concerned  with  a  very  old  fiber-system,  one  very  important 
for  the  entire  mechanism  of  the  brain.  For  in  all  vertebrates,  from  fishes 
up  to  mammals,  there  may  be  demonstrated  a  well-defined  bundle  of  fibers, 
which  arises  in  the  corpus  striatum  and  in  part  terminates  in  a  nucleus  of 
the  interbrain,  in  part  passes  on  farther  down.  In  man  it  is  to  be  found 
with  difficulty,  because  so  many  tracts  from  the  mantle  region  are  associated 
with  it.  Yet  I  have  recognized  this  basal  bundle  of  the  forebrain  in  young 


CAPSULA   INTERNA,    CORPUS    STRIATUM,    INTERBRAIN-GANGLIA.        257 

embryos,  and  it  is  probably  the  fibers  of  this  bundle  which  Wernicke  and 
Flechsig  have  described  as  arising  from  the  corpus  striatum.  The  latter  has 
also  recognized  the  connection  with  the  thalamus.  It  has  already  been 
described  in  the  chapters  on  comparative  anatomy  and  there  designated  as 
the  tractus  strio-thalamicus. 

Recently,  however,  I  have  succeeded  in  fully  establishing  the  course  of  the 
tracts  arising  from  the  corpus  striatum  in  the  brain  of  a  dog  from  which  the  cortex 
had  been  completely  removed.  In  this  animal  experimented  upon,  all  of  the  fibers 
of  the  corona  radiata  coming  from  the  cortex  were  secondarily  degenerated  and  had 
almost  disappeared.  It  was  there  recognized  with  all  certainty  that  very  large  fiber- 
masses  developed  from  the  head  of  the  nucleus  caudatus  and  from  the  putamen, 
which  passed  toward  the  base  and  at  the  same  time  somewhat  posteriorly  in  the 
anterior  division  of  the  internal  capsule.  The  greatest  part  of  this  fiber-mass  turned 
inwardly  at  once  and  was  lost  in  the  thalamic  ganglia.  The  part  that  extended 
farther  downward  gradually  passed  toward  the  median  line  to  disappear  in  the  gan- 
glia in  the  region  below  and  behind  the  thalamus.  In  the  region  posterior  to  the 
corpora  quadrigemina,  the  entire  fiber-system,  anteriorly  so  large,  had  passed  over 
into  the  ganglia.  Its  last  tracts  were  taken  up  by  the  substantia  nigra.  The  re- 
searches by  Maliaim  and  by  Monakoiv  upon  the  secondary  degenerations  appearing 
after  disease  in  the  neighborhood  of  the  corpus  striatum  show  that  in  man  also  the 
fiber-system  arising  there  has  the  relations  represented  in  the  diagram  opposite. 

The  radiatio  strio-thalamica  forms,  therefore,  a  large  and  important  con- 
necting pathway  between  the  corpus  striatum  and  the  ganglia  of  the  interbrain 
and  midbrain. 

The  fibers  of  the  tegmental  radiation,  from  the  cortex,  pass  between  the 
divisions  of  the  globus  pallidus.  They  pass  through  this  as  white  lines, 
and  collect  at  the  base  of  the  lenticular  nucleus  to  form  a  definite  bundle  of 
fibers,  which  is  dorsal  to  the  ansa  lentiformis  and  passes  mesially  exactly 
like  this.  It  later  extends  into  the  medulla  oblongata. 

Most  of  the  fibers  of  the  tegmental  radiation  pass  mesially  into  the 
region  which  lies  under  the  thalamus  opticus  and  is  named  the  regio  sub- 
thalamica. 

The  accompanying  illustration,  a  section  through  the  brain  of  a  fetus  of  8 
months,  shows  the  relation  of  the  tegmental  fibers  to  the  lenticular  nucleus.  Ex- 
cepting the  fibers  represented,  there  are  no  other  medullated  fibers  present  in  the 
entire  cerebrum  at  this  embryonic  stage.  The  fibers,  in  particular,  which  arise  in 
the  nucleus  caudatus  and  the  putamen  are  still  entirely  wanting.  Only  after  the 
investigation  of  the  fetal  brain  was  it  possible  to  explain  with  certainty  the  relation 
of  the  lenticular  nucleus  and  the  tegmental  radiation  to  one  another. 

In  mammals  there  exists  a  small  fiber-tract  which  passes  laterally  along 
the  entire  extent  of  the  nucleus  caudatus.  It  begins  in  front  of  the  head 
of  this  ganglion  as  a  few  fibers  which  appear  to  come  out  of  the  head  itself. 
The  tract  increases  more  and  more  in  size  posteriorly,  but  becomes  smaller 


258 


ANATOMY   OF   THE    CENTRAL    NERVOUS    SYSTEM. 


in  consequence  of  the  slenderness  of  the  tail  of  the  nucleus,  and  is  to  be 
traced  no  farther  than  the  nucleus  itself.  The  bundle  lies  in  the  angle 
between  the  surface  of  the  nucleus  caudatus  and  the  roof  of  the  ventricle; 
the  fibers  of  the  corpus  callosum  radiate  directly  over  it.  The  fibers  of  the 
bundle  appear  to  me  to  come  from  the  nucleus  caudatus  itself,  and  to  return 
into  it  again.  It  is  called  the  association-bundle  of  the  nucleus  caudatus 
(Sachs);  but  I  cannot  sharply  separate  it  from  the  fronto-occipital  associa- 
tion-bundle, which  lies  close  to  it. 

You  have  now  become  acquainted  with  the  origin  and  the  proximal 
part  of  a  large  number  of  the  fibers  which  go  to  make  up  the  forebrain. 


Fig.  167. — Frontal  section  through  the  brain  of  a  fetus  of  about  thirty- 
two  weeks.  All  medullated  nerve-fibers  stained  black  by  haematoxylin.  Teg- 
mental  radiation  (above)3  ansa  lentiformis  (below),  and  anterior  commissure 
(below  and  external)  are  medullated.  No  medullated  fibers  are  as  yet  seen  in 
the  putamen  and  the  nucleus  caudatus. 


Let  us  now  turn  to  the  regions  where  the  majority  of  the  medullated  tracts 
.of  the  cerebrum  terminate. 

Back  of  the  cerebrum  lies  the  interbrain.  Its  lateral  walls  are  the 
thalami  optici.  These  consist  of  several  gray  nuclei,  which  are  not  sharply 
separated  from  one  another.  White  medullated  fibers,  the  stratum  zonale, 
cover  the  thalamus.  They  may  be  traced,  on  the  one  hand,  in  a  direction 
toward  the  base  of  the  brain  into  the  optic  nerves;  on  the  other  hand,  they 


CAPSULA    INTERNA,    CORPUS    STRIATUM,    INTERBRAIN-GANGLIA.        259 

appear  to  arise  from  the  posterior  parts  of  the  capsula  interna,  perhaps  from 
the  optic  radiation.  All  pass  into -the  depths  of  the  thalamus,  where  they 
collect  into  bundles  between  the  thalamic  ganglia,  and  thus  apparently 
separate  these  from  one  another.  Microscopic  investigation  shows  that  they 
penetrate  into  the  fine  net-work  of  nerve-fibers  which  pervades  these  ganglia. 
There  may  be  distinguished  in  each  thalamus:  a  mesial  (inner)  nucleus, 
which  projects  into  the  ventricle;  a  lateral  (outer)  nucleus;  and,  between 
these,  the  anterior  nucleus.  The  lateral  nucleus  is  the  largest.  The  anterior 
nucleus,  with  its  blunt  end  directed  anteriorly,  appears  as  a  wedge  driven  in 
between  the  other  two.  This  anterior,  thicker  end,  which  is  visible  an- 
teriorly as  an  elevation  on  the  surface  of  the  thalamus,  has  been  met  with 
earlier  under  the  name  of  tuberculum  anterius. 

The  pulvinar  borders  on  the  mesial  nucleus,  and  is  not  easily  separable 
from  it  in  man.  It  is  a  huge  "cushion"  (Polster)  which,  occupying  the  en- 
tire posterior  division  of  the  thalamus,  projects  like  a  tumor  (Wulst)  into 
the  ventricle.  On  the  median  border  of  the  inner  nucleus  lies  the  ganglion 
habenulce,  previously  mentioned. 

Monakow,  who  has  recently  studied  the  thalamic  nuclei  more  thor- 
oughly, proposes,  on  account  of  the  structure  and  the  entering  radiations, 
to  separate  the  ventral  region  of  the  lateral  nucleus  and  designate  it,  along 
with  several  other-  small  nuclei-groups  which  are  also  situated  ventrally,  as 
the  ventral  nucleus  of  the  thalamus.  On  the  thalamus  posteriorly  there 
lies,  ventral  and  external  to  the  pulvinar,  a  ganglion  of  a  peculiar  grayish 
appearance:  the  corpus  geniculatum  laterale.  It  projects  far  into  the  sub- 
stance of  the  thalamus,  and  gives  origin  to  a  large  number  of  fibers  of  the 
tractus  opticus. 

Externally,  the  optic  thalamus  borders  on  the  internal  capsule  (Fig. 
160).  Numerous  tracts,  the  corona  radiata  of  the  flialamus,  pass  from  the 
capsule  into  the  thalamus.  They  come  from  various  directions  and  cross 
one  another  as  they  converge  into  the  thalamus.  Masses  of  gray  matter  are 
found  within  the  net-work  of  crossing  fibers.  The  outer  zone,  containing 
these  crossed  fibers,  is,  from  its  appearance,  designated  as  the  "latticed" 
layer  (Gitterschicht).  Since  most  of  the  medullated  fibers  converge  into  the 
lateral  nucleus,  this  thus  appears  lighter  than  the  other  thalamic  nuclei. 

The  thalamic  ganglia  atrophy,  to  a  large  extent,  if  the  cortical  region 
from  which  they  receive  their  converging  fibers  degenerates  or  is  removed. 
The  investigations  by  Monakow,  especially  directed  toward  these  relations, 
show  that  the  most  anterior  and  mesial  divisions  of  the  thalamus  are  con- 
nected with  the  convolution-groups  of  the  frontal  lobe,  the  lateral  nuclear 
groups  with  the  parietal  convolutions,  and  the  ventral  nuclei  with  the 
operculum.  At  present  not  the  least  is  known  concerning  the  physiological 
significance  of  these  pathways.  Some  of  the  other  thalamic  radiations  are 


260  ANATOMY   OF    THE    CENTEAL   NERVOUS    SYSTEM. 

now  better  understood.  First  of  all,  there  are  the  fibers  from  the  parietal 
region  to  the  ventral  nucleus.  They  must  contain,  as  I  have  previously 
stated,  that  portion  of  the  sensory  fiber-system  which  passes  to  the  cortex 
from  this  nucleus,  where  a  part  of  the  fillet  terminates.  Then  we  know  that 
the  greatest  part  of  the  fibers  converging  into  the  posterior  divisions  of  the 
thalamus,  especially  into  the  pulvinar  and  the  corpus  geniculatum  laterale, 
arises  from  the  occipital  lobe,  and  represents  the  secondary  pathway  from 
the  primary  optic  terminals  to  the  cortex. 

The  inner  side  of  the  thalamus  is  separated  from  the  ventricle  by  a 
uniform  layer  of  gray  matter.  This  is  called  the  central  gray  matter  of  the 
middle  (third)  ventricle,  and  consists  of  a  tissue  rich  in  cells  and  traversed 
in  all  directions  by  numerous  fine,  medullated  nerve-fibers. 

ScMtz,  who  has  made  this  gray  matter  a  subject  of  especial  study  in  man, 
found  that  it  contains  afferent  tracts  from  almost  all  of  the  ganglia  surrounding  the 
third  ventricle,  and,  what  is  particularly  interesting,  that  it  degenerates  like  the 
fibers  of  the  cerebral  cortex  in  progressive  paralyses.  A  tract  of  fine,  medullated 
fibers,  which  may  be  traced  in  the  gray  matter  from  the  third  ventricle  down  as  far 
as  the  nuclei  of  the  hypoglossus,  has  been  named  by  him  the  dorsal  longitudinal 
bundle  of  the  central  gray  matter.  It  is,  for  the  most  part,  especially  well  defined, 
and  constantly  lies  close  under  the  epithelium  of  the  ventricle. 

In  the  median  line  of  the  brain  the  central  gray  matter  forms  the  floor 
of  the  ventricle.  There  here  run  across  in  it  from  one  side  of  the  brain  to 
the  other  several  slender  tracts  of  fibers.  One  of  these,  Meynert's  commis- 
sure, is  better  defined  than  the  others.  Its  origin  and  destination  are  not 
sufficiently  well  known.  It  was  retained  in  the  dog  after  complete  destruc- 
tion of  the  cortex.  Gudden's  commissure,  lying  anterior  and  ventral  to  it, 
we  will  become  better  acquainted  with  later.  In  reptiles,  Meynert's  com- 
missure arises  from  the  giant-celled  nucleus  of  the  central  gray  matter. 

The  central  gray  matter  on  the  mesial  surface  of  the  thalamus  unites 
with  that  of  the  opposite  side  for  a  distance  of  about  three-fourths  of  a 
centimeter  to  form  the  commissura  mollis,  or  media. 

In  man  few  medullated  fibers  run  in  it.  Whether  a  commissure  which 
is  present  in  lower  vertebrates  in  an  analogous  location,  and  which  is  much 
richer  in  fibers,  is  identical  with  the  commissura  media  still  remains  to  be 
determined  (see  Fig.  82). 

Nissl  has  shown  for  the  rabbit  that  each  of  the  thalamic  nuclei  is  again  divided 
into  from  three  to  four  subnuclei,  which  are  easily  distinguishable  from  one  another 
by  the  behavior  of  their  cells  toward  stains.  Moreover,  he  has  described  in  this 
animal:  a  nucleus  of  the  "latticed"  layer  and,  anterior  to  the  ganglion  habenulae, 
the  nucleus  of  the  median  line.  To  these,  then,  there  might  still  be  added  the  small 
nucleus  magno-cellularis,  found  in  the  most  anterior  planes  of  the  thalamus.  Monakow 
has  shown  that  the  corpus  geniculatum  laterale  is  divided  into  five  nuclei:  a  dorsal 


CAPSULA   INTEKNA,    CORPUS    STEIATUM,    INTERBRAIN-GANGLIA.        261 

and  a  ventral  nucleus  which  are  each  subdivided  into  two,  and  a  latero-ventral 
nucleus.  Of  these  nuclei,  the  posterior  division  of  the  dorsal  nucleus  belongs  to 
the  retinal  fiber-system,  while  the  remaining  nuclei  receive  afferent  tracts  from  the 
cortex  to  the  primary  optic  terminals.  Each  of  these  latter  nuclei  stands  in  relation 
with  a  definite  portion  of  the  visual  system. 


Fig.  168. — Frontal  section  through  the  brain  just  behind  the  chiasma. 
Diagrammatic.  Ccntr.  Hohlengrau,  Central  gray  matter  of  the  ventricle.  Gitter- 
schicht,  Latticed  layer.  Haubenfaserung,  Tegmental  fiber-system.  Lins.  K. 
Schlinge,  Ansa  lentiformis.  Stabkranz  zum  Thalamus,  Corona  radiata  to  the 
thalamus.  Unterer  Thalamus  Stiel,  Inferior  pedicle  of  the  thalamus.  Zur 
ScMeife,  To  the  fillet. 


The  thalamus  is  essentially  a  "receiving-station":  on  the  one  hand,  for 
the  fibers  from  the  cerebral  cortex — the  corona  radiata  of  the  thalamus;  on  the 
other  hand,  for  the  fibers  from  the  corpus  striatum — radiatio  sir io-thal arnica, 


262  ANATOMY    OF   THE    CENTRAL    NERVOUS    SYSTEM. 

ansa  lentiformis,  etc.    In  proportion  to  its  enormous  mass,  the  thalamus  sends 
only  a  few  fibers  downward. 

The  tracts  arising  from  the  ganglia  run,  for  the  greater  part,  in  two, 
white,  transverse  lamina,  passing  through  their  mass:  the  lamina  medullaris 
externa  and  interna.  The  thalamic  fibers  extend  farther  downward  only  to  a 
very  limited  extent.  Essentially  but  a  single  bundle,  the  superior  fillet,  corn- 


Fig.  169. —  (From  the  dog.)  Frontal  section  which  passes  approximately 
through  the  anterior  third  of  the  thalamus.  Like  the  following  sections,  it  re- 
quires only  a  few  words  by  way  of  supplementary  explanation,  since  all  the  parts 
are  lettered.  To  the  right  and  above,  the  fibers  from  the  mantle  pass  down  into 
the  internal  capsule,  lateral  to  the  corpus  striatum.  They  there  meet  with  the 
large  fiber-system  from  the  nucleus  caudatus,  penetrate  it,  and  converge,  in  part, 
as  the  corona  radiata  into  the  lateral  thalamic  ganglion.  Most  of  the  fibers,  how- 
ever, remain  in  the  position  named,  and  pass  backward.  This  part  must  be 
surrounded  by  the  fiber-system  of  the  corpus  striatum,  when  the  same  passes 
inward  to  its  terminal  in  the  ganglia  of  the  interbrain.  To  the  tracts  thus  em- 
bracing the  fibers  there  are  added — close  to  the  base — the  tracts  from  the  puta- 
men,  which  form  with  those  the  ansa  lentiformis.  Mesial  to  the  bundle  of  the 
ansa,  already  met  with  here,  lies  the  slender  radiation  passing  from  the  olfactory 
field  to  the  corpus  mamillare.  From  the  olfactory  radiation  there  is  given  off 
at  this  level,  and  farther  posteriorly,  the  bundle  of  the  tsenia  thalami,  which 
ascends  dorsally.  This  is  seen  to  pass  as  far  as  the  surface  of  the  thalamus  and 
then  to  turn  backward  to  the  ganglion  habenulse.  The  bundle  of  Vicq  d'Azyr 
probably  belongs  to  the  olfactory  apparatus  also;  it  develops  from  the  medullary 
capsule  of  the  anterior  thalamic  nucleus,  which  is  here  cut  in  the  section. 
Faserung  d.  Stammgangl.,  Fiber-system  of  the  corpus  striatum.  Rieclibdl  Zw. 
H.,  Olfactory  bundle,  interbrain.  Stabkranz  aus  Cortex,  Corona  radiata  from 
cortex.  Stabkranz  z.  N.  lot.,  Corona  radiata  to  nucleus  lateralis. 


CAPSULA    INTEKXA,    COKPUS    STRIATUM,    INTERBRAIN-GANGLIA.     .    263 

ing  from  the  stria  medullaris  externa  and  particularly  from  the  ventral 
nucleus,  may  be  traced  as  far  as  the  end  of  the  oblongata,  perhaps  into  the 
lateral  columns  of  the  spinal  cord  also.  The  stria  medullaris  interna  is  not 
traceable  beyond  the  midbrain.  From  the  most  posterior  thalamic  region 
arises  the  radiatio  thalami  ventralis,  the  termination  of  which  is  entirely 
unknown  (oblongata — lateral  columns  of  cord). 

On  the  accompanying  very  diagrammatic  illustration  (Fig.  168)  is  to  be 
studied  the  relation  of  the  thalamus  to  the  base  of  the  brain,  to  the  central 
ventricular  gray  matter,  to  the  capsula  interna,  and  to  the  nucleus  lenti- 
formis. 

You  will  observe  something  in  this  section  that  until  now  could  merely 
be  mentioned  cursorily.  It  is  the  region  internal  to  the  lenticular  nucleus 
and  ventral  to  the  thalamus.  There  are  collected  here  several  fiber-strands, 
running  somewhat  parallel  with  one  another,  which,  in  part,  cross  the  in- 
ferior portion  of  the  capsula  interna, at  an  angle,  in  part  pass  on  over  it. 
Those  fibers  which  are  superior  belong  to  the  lenticular  fiber-system;  they 
form  the  ansa  lentiformis,  previously  mentioned.  The  inferior  fibers  are 
the  coronal  fibers  to  the  thalamus,  which  come  from  the  occipital  and  tem- 
poral lobes;  they  are  designated  as  the  inferior  pedicle  of  the  thalamus 
(u.  s.,  Fig.  159).  The  entire  mass  of  fibers  met  with  in  section  in  Fig.  168 
ventral  to  the  nucleus  lentiformis  is  called  the  substantia  innominata. 
Just  behind  the  substantia  innominata  the  fibers  of  the  capsule,  which  be- 
come the  pes  pedunculi,  or  crusta,  emerge  at  the  base  of  the  brain.  The 
substantia  innominata  bounds  the  crus  cerebri  at  the  anterior  end.  It  re- 
sembles a  loop  laid  over  the  peduncle  in  front,  and  is  therefore  designated 
as  the  ansa  peduncularis. 

The  diagram  (Fig.  159),  moreover,  departs  so  far  from  the  real  appear- 
ance that  it  will  be  advantageous  to  give  some  attention  to  the  opposite 
illustration  of  an  actual  section  through  the  thalamus  of  a  dog  (Fig.  169). 

From  this  and  the  following  illustrations  you  will  obtain  a  better  idea  of  the 
structure  of  the  inter  brain  than  I  could  give  you  heretofore.  They  contain 
somewhat  more  details  (pedicles  of  the  thalamic  nuclei,  etc.)  than  were  mentioned 
in  the  text,  because  they  are  intended  to  afford  an  opportunity  to  study  actual  sec- 
tions more  closely.  I  beg  to  make  use  of  these  illustrations  again  at  the  end  of  this 
and  the  next  chapter. 

In  the  preceding  two  chapters  it  was  necessary  to  describe  so  many 
brain-structures  by  themselves  that  I  fear  I  can  hardly  have  succeeded  in 
giving  you  a  correct  idea  of  the  relation  of  these  -parts  as  a  whole  and  to  one 
another.  Such  a  conception  must  be  thoroughly  acquired,  however,  because 
even  a  better  knowledge  than  I  have  been  able  to  give  you  of  the  fiber- 
systems  and  ganglia  will  be  of  little  value  when  you  come  to  study  a  brain 
topographically.  The  time  has  arrived,  then,  when  I  must  demonstrate  to 


264 


ANATOMY    OF    THE    CENTRAL    NERVOUS    SYSTEM. 


you  a  series  of  frontal  sections  through  an  adult  brain.     They  may  serve 
as  a  guide  in  your  own  investigations. 

For  topographical  study  I  advise  you  to  place  an  entire,  uncut  brain  in  10- 
per-cent.  formol  solution  (Blum),  and,  after  from  four  to  eight  days,  to  cut  it  up 
with  a  razor  into  sections  about  one  centimeter  in  thickness.  The  illustrations  which 
I  here  present  to  you  are  made  from  sections  prepared  in  this  manner.  Here  and 
there  an  examination  in  water  with  the  lens  will  prove  advantageous. 

The  first  section  that  I  make  (not  shown  here)  passes  a  few  centimeters  behind 
the  frontal  pole  of  the  brain.  Surrounded  by  the  convolutions,  which  are  here  small, 


(  Fasc.  area 
-    1     atus 


{Adcnisnnt 
capsula) 
int. 


Gyri  orbitales 


Fig.  170. 


it  contains  an  homogeneous  white  mass  constituted  essentially  as  follows:  Just 
under  the  cortex  it  is  composed  of  short  association-bundles;  beneath  these  of  the 
coronal  fibers  to  the  thalamus  and  to  the  pons  (which  begin  to  pass  downward  even 
here) ;  and,  finally,  of  the  frontal  ends  of  the  longer  association-systems. 

The  second  section  (Fig.  .170)  is  made  a  few  millimeters  behind  the  beginning 
of  the  corpus  callosum.  It  just  cuts  through  the  genu  of  the  corpus  callosum,  the 
most  anterior  fibers  connecting  both  hemispheres.  A  great  part  of  these  fibers  is 
cut  away  laterally;  it  is  those  fibers  which  turn  anteriorly  in  a  gentle  curve,  and 
thus  naturally  are  chiefly  contained  in  the  portion  of  brain  removed.  Directly  lateral 
to  the  fibers  of  the  corpus  callosum  there  is  cut  the  gray  substance  which  surrounds 


CAPSULA    INTERNA,    CORPUS    STRIATUM,    INTERBRAIN-GANGLIA.        265 

the  lateral  ventricle;  that  is  to  say,  its  anterior  horn.  Indeed,  at  several  points, 
the  ventricle  itself  has  been  opened. 

The  white,  medtiUary  sitbstance  lateral  to  the  ectoventricular  gray  substance 
is  formed,  first  of  all,  by  the  tracts  from  the  frontal  lobe  to  the  anterior  limb  of  the 
internal  capsule.  It  is  approximately  the  region  which  is  designated  "Ad  crus  ant." 
This  bundle,  cut  transversely,  is  then  surrounded  ventrally,  and  in  part  split  up  and 
interlaced,  by  fibers  of  the  corpus  callosum  and  by  long  association-fibers,  which 
belong  to  the  fasciculus  uncinatus. 

Dorsal  to  it  lies  the  region  (indicated  by  light  shading  in  the  illustration)  in 
which  the  fasciculus  arcuatus  spreads  out.  In  addition  to  this  there  are  next,  close 


Stria  longitnd. 
Ventricnlus  lat. 
Septum  pellucid. 
Caput  nucl.  caud. 

Caps.  int.  eras  ant. 
Rostrum  corp.  callos. 


Fasc.  fronto-occip. 

/Region  of  hypoglossal 
X   and  speech-pathway 

Putamen 


Fiss.  Sylvii  insulse 
Capsula  ext. 
Claustrum 
Regio  fasc.  uncin. 


Fig.    171. 


under  the  cortex,  the  curved  tracts  of  the  short  association-pathways.  Over  the 
entire  area  there  are  disposed  numerous  fibers,  which  pass,  in  part,  to  the  thalamus; 
in  part,  have  an  unknown  course.  There  is  probably  quite  a  number  of  association- 
pathways  here  also.  Even  in  the  plane  of  this  section,  in  specimens  hardened  in 
chrome-salts,  the  cingulum  may  be  met  with,  cut  transversely,  just  above  and  below 
the  corpus  callosum;  and,  dorso-mesial  to  the  fibers  of  the  corona  radiata  passing 
to  the  internal  capsule,  is  also  met  the  anterior  radiation  of  the  fronto- occipital 
association-bundle. 

The  next  section  (Fig.  171)  is  made  just  behind  the  genu  of  the  corpus  callosum. 
Dorsally,  it  passes  through  the  body  of  the  corpus  callosum,  ventrally  it  cuts  the 


266 


ANATOMY    OF   THE    CENTRAL   NERVOUS    SYSTEM. 


most  posterior  portion  of  the  inferior  limb  of  the  corpus  callosum,  the  rostrum. 
Between  these  two  parts  lies  the  inner  wall  of  the  hemisphere,  the  ventral  portion 
of  which  is  designated  as  the  area  Brocse,  the  more  dorsal  part  as  the  septum  pel- 
lucidum.  The  ventriculus  septi  is  visible  between  the  two  walls  of  the  septum. 
The  anterior  horn  of  the  ventricle  is  now  widely  opened,  and  the  head  of  the  nucleus 
caudatus  is  cut  through  its  greatest  expanse.  Lateral  to  this  the  fibers  of  the  in- 
ternal capsule  pass  down  from  the  frontal  pole,  with  which  there  is  associated  in 
exactly  this  region  the  large  fiber-system  passing  from  the  nucleus  caudatus  to  the 
thalamus,  the  radiatio  strio-thalamica. 


Fig.  172. 

Externally  to  the  internal  capsule,  here  still  interrupted  by  many  bands  of 
gray  matter,  lies  the  most  anterior  part  of  the  putamen.  Then  follows  laterally 
the  capsula  externa,  the  claustrum,  and  the  medulla  and  cortex  of  the  insula.  The 
fasciculus  uncinatus  is  lost  in  the  first.  This  section  already  strikes  the  anterior 
end  of  the  Sylvian  fissure. 

The  entire  dorsal  half  of  the  section'  is  occupied  by  the  medullary  masses  that 
here  arise  from  the  three  frontal  convolutions. 

They  consist,  for  the  most  part,  of  association-fibers  that  connect  the  regions 
of  the  hemisphere  with  one  another,  more  especially  such  fibers  as  belong  to  the 
frontal  lobe  itself,  but  there  are  some  longer  fibers  also,  as  the  fasciculus  arcuatus 


CAPSULA   INTERNA,    CORPUS    STRIATUM,    INTERBRAIN-GANGLIA.        267 

and  the  fronto-occipital  association-bundle.  Besides  these,  the  entire  white  medullary 
substance  is  here  traversed  by  fibers  of  the  corpus  callosum.  Only  a  few  white  fibers 
pass  from  this  region  into  the  capsula  interna.  Of  the  tracts  that  are  important 
clinically  there  are  essentially  only  the  coronal  fibers  from  the  facialis  and  hypo- 
glossus  centers,  and  the  speech-patliAvay,  the  transverse  section  of  which  is  to  be 
assumed  as  lying  somewhat  lateral  to  the  fasciculus  fronto-occipitalis.  The  ventral, 
cortical  region  belongs  to  the  gyri  orbitales,  over  which  the  olfactory  lobe  passes. 

A  section  made  only  a  little  farther  back  passes  through  the  most  posterior 
part  of  the  septum  pellucidum,  and  now  cuts  the  pillars  of  the  fornix,  which  ascend 
there.  I  demonstrate  such  a  transverse  section  (Fig.  172),  because  it  is  also  well 
adapted  to  show  the  course  of  the  commissura  anterior,  the  decrease  in  size  of  the 
head  of  the  nucleus  caudatus,  and  the  increase  in  that  of  the  lenticular  nucleus. 

The  triangular,  gray  mass  between  the  commissure  and  the  caudate  nucleus 
by  this  time  belongs  to  the  central  gray  matter  which  covers  over  the  thalamus. 
The  white  fiber-tract  that  covers  this  mass  and  projects  free  into  the  ventricle  is 
the  stria  terminalis,  especially  that  part  of  the  same  which  arises  from  the  anterior 
commissure. 

Just  posteriorly  there  lie  in  the  same  relation,  and  having  a  similar  course,  the 
tracts  of  the  tsenia  thalami.  Ventrally,  the  olfactory  area  begins-  to  appear. 

A  section  made  exactly  where  the  olfactory  lobe  becomes  intimately  connected 
with  the  base  of  the  brain  (Fig.  173)  strikes,  farther  dorsally,  the  posterior  portion 
of  the  septum,  where  are  found  the  posterior  pillars  of  the  fornix.  These  have 
reached  their  present  position  from  the  postero-ventral  region  of  the  brain.  Their 
transverse  sections  will  be  met  with  in  all  the  succeeding  illustrations  until  here 
in  front,  where  they  turn  toward  the  base  of  the  brain  and  pass  ventrally  into  the 
central  gray  matter  of  the  ventricle.  Their  oval  frontal  sections  lie  in  the  gray 
matter  directly  in  front  of  the  transverse  fibers  of  the  commissura  anterior. 

The  lateral  ventricle,  here  only  a  fissure,  lies  lateral  to  the  pillars  of  the  fornix; 
into  it  projects  the  most  anterior  portion  of  the  thalamus,  the  nucleus  anterior. 
This  is  covered  over  by  white  fibers,  which  penetrate  into  its  interior,  and  here 
separate  it  from  the  nucleus  lateralis  thalami.  The  thalamus  here  receives  fibers  at 
its  lateral  and  at  its  ventral  surfaces.  The  lateral  fibers  come  from  the  capsula 
interna  and  belong,  the  same  as  the  ventral  fibers,  to  the  fiber-systems  coming  from 
the  cortex,  as  well  as  from  the  corpus  striatum.  Those  fiber-tracts,  especially,  which 
enter  at  the  ventral  end  are  plainly  formed  by  the  inferior  pedicle  from  the  temporal 
lobe  and  the  lenticular  loop  from  the  corpus  striatum. 

In  the  plane  of  this  section  the  fibers  from  the  anterior  central  gyrus  have 
in  large  part  become  mingled  with  those  of  the  internal  capsule.  This  now  contains 
at  least  the  coronal  fibers  for  sight,  the  motor  speech-pathway,  the  hypoglossus  and 
a  part  of  the  pyramidal  fiber-system  for  the  arm  and  hand.  Fibers  from  the  caudate 
nucleus,  which  run  ventro-posteriorly,  pass  through  its  tracts  arising  from  the 
mantle.  The  white  medullary  substance  is  still  formed  essentially  as  in  the  previous 
sections. 

Lateral  to  the  capsula  interna  there  is  now  met  with  the  greatest  expanse  of 
the  corpus  striatum:  the  putamen  and  the  two  divisions  of  the  globus  pallidus. 

Numerous  medullary  radiations  arise  in  the  first;  they  pass,  in  large  part,  into 
the  lenticular  loop  (ansa  lentiformis) .  Ventral  to  the  corpus  striatum  the  trans- 
verse section  of  the  commissura  anterior  is  recognized.  It  lies  just  over  the  olfactory 
formation,  the  cortex  and  medulla  of  which  may  here,  indeed,  be  separated  from  one 
another.  The  entrance  of  the  olfactory  radiation  into  this  is  to  be  recognized. 
From  this  region  the  ta^nia  thalami  rises  dorsally  and  enters  the  layer  of  white 


268 


ANATOMY    OF    THE    CENTRAL    NERVOUS    SYSTEM. 


matter  covering  the  mesial  side  of  the  thalamus.     Yet  its  entire  course  is  not  to  be 
seen  in  this  section. 

The  fifth  section  (Fig.  174)  is  made  directly  anterior  to  the  chiasma.  This  is 
not  divided,  however,  but  is  turned  ventrally.  The  narrow,  fissure-like  ventricle  is 
lengthened  ventrally  to  form  the  infundibulum.  In  its  inferior  third  it  is  crossed 
by  the  commissura  media.  The  thalami,  covered  by  the  stratum  zonale  and  the 
taenia,  project  into  it,  and  it  is  closed  above  by  the  columns  of  the  fornix,  over  which 


Lob.  temporal!* 


Fig. 


lies  the  corpus  callosum.  The  lateral  end  of  each  column  is  directly  continuous,  as 
Fig.  173  shows,  with  the  plexus  chorioideus  of  the  lateral  ventricle.  Close  by  the  side 
of  the  commissura  mollis  the  descending  columns  of  the  fornix  are  seen,  cut  trans- 
versely, in  the  central  gray  matter.  Traversing  the  gray  matter  of  the  infundib- 
ulum, they  here  turn  posteriorly  and  ventrally  to  the  corpus  mamillare. 

Of  the  thalamus  there  is  now  visible  the  nucleus  anterior,  the  nucleus  medialis, 
and  the  nucleus  lateralis — also  the  latticed  layer.  From  the  first  there  develops  the 
tractus  thalamo-mamillaris,  the  bundle  of  Vicq  d'Azyr.  The  fibers  from  which  it 


CAPSULA   INTERNA,    CORPUS    STRIATUM,    INTERBEAIN-GANGLIA.        269 

originates  and  fibers  from  the  stratum  zonale,  as  well  as  fibers  of  a  still  unknown 
origin,  together  form  a  proper  medullary  capsule  around  the  nucleus  anterior.  The 
lateral  part  of  this  capsule,  and  a  portion  of  the  ventral,  may  be  traced  far  back- 
ward as  the  lamina  medullaris  interna  thalami. 

The  tail  of  the  nucleus  caudatus  of  the  corpus  striatum  is  visible  dorsally  and 
ventrally.  On  its  mesial  side  it  has  the  tract  of  the  stria  terminalis.  Besides  this 
part  of  the  corpus  striatum  there  is  visible  the  lenticular  nucleus  with  its  three 
divisions,  from  which  the  fibers  of  the  ansa  lentiformis  are  seen  to  develop  at  pre- 
cisely this  level. 

These  fibers  pass  to  the  basal  part  of  the  capsula  interna,  which  they  cross  to 
enter  the  thalamic  ganglia  from  below.  For  almost  this  entire  distance  they  lie 
upon  the  fiber-system,  which  likewise  passes  into  the  thalamus,  as  the  inferior  thal- 
amic pedicle,  from  the  temporal  lobe.  • 

The  internal  capsule  here  contains  nearly  the  entire  motor  fiber-system.  More- 
over, it  contains  the  pathways  from  the  frontal  lobe  to  the  pons.  Many  coronal  fibers 


Fig.  174. 


pass  from  it  into  the  thalamus.  The  motor  speech-pathway  still  lies  in  the  same 
place  as  in  the  preceding  figure.  Ventral  to  the  lenticular  nucleus  lies  the  com- 
missura  anterior,  and  under  this  we  see  the  nucleus  amygdalae. 

The  optic  thalami  everywhere  lie  so  close  upon  the  internal  capsule  that  dis- 
eases only  rarely  come  under  observation  in  which  the  thalami  alone  are  involved. 
Even  in  these  it  often  remains  doubtful  how  many  of  the  phenomena  which  appear 
are  to  be  referred  to  the  thalami,  since  the  function  of  the  neighboring  fibers  of  the 
capsula  interna  was  impaired  indirectly.  For  this  reason  it  has  not  yet  been  possible 
accurately  to  determine  the  symptoms  that  are  produced  by  disease  of  the  optic 
thalamus.  According  to  Meynert,  the  innervation  sensations  of  the  upper  extremi- 
ties are  thereby  disturbed.  In  this  manner  are  said  to  arise  the  delusive  ideas  con- 
cerning the  position  of  these  members,  and  from  these  ideas,  again,  the  forced  posi- 
tions. Motor  paralysis  is  probably  not  produced  by  destruction  of  the  thalamus; 
just  as  little,  sensory  paralysis.  Disturbances  of  sight  in  the  form  of  homonymous 
lateral  hemianopsia,  perhaps  of  crossed  amblyopia  also,  were  repeatedly  observed. 


270  ANATOMY    OF   THE    CENTKAL    NERVOUS    SYSTEM. 

Likewise  in  disease  of  the  optic  thalami,  the  symptoms  of  hemichorea,  of  athetosis, 
and  of  unilateral  tremor  Avere  observed  not  very  infrequently.  These  have  also  been 
observed  following  lesions  of  other  parts  of  the  brain,  yet  were  commonly  concerned 
with  fiber-systems  connected  with  the  thalamus. 

The  same  difficulty  presents  itself  when  an  attempt  is  made  to  determine  the 
symptoms  of  disease  of  the  corpus  striatum.  What  was  for  a  long  time  described 
as  such  (hemiplegia,  for  example)  may  arise  just  as  well  through  the  involvement 
of  the  neighboring  capsula  interna.  A  case  is  known  of  the  destruction  of  both 
putamina  which  terminated  without  a  symptom  referable  thereto. 


CHAPTEE    XVII. 

METATHALAMUS  AND  HYPOTHALAMUS. 

THE  EEGIO  SUBTHALAMICA  AND  THE  STRUCTURES  AT  THE  BASE  OF 

THE    BRAIN. 

AT  the  end  of  the  last  chapter  we  had  approached  a  region  of  the  brain 
which,  extraordinarily  complicated  in  structure,  hitherto  belonged  to  the 
parts  of  the  brain  that  were  least  understood  and  explained.  I  now  purpose 
to  bring  before  you  the  most  important  structures  of  this  regio  subthalamica. 

If  you  examine  Fig.  173  or  Fig.  174  it  is  apparent  that  the  thalamus 


Fig.  175. — Section  through  the  regio  subthalamica. 


lies  upon  the  internal  capsule.  Farther  posteriorly  this  relation  ceases. 
Several  small,  gray  ganglionic  masses  shift  between  it  and  the  internal  cap- 
sule, into  which  masses  converge  numerous  fiber-tracts  from  the  nucleus 
lentiformis,  from  the  capsula  interna,  and  from  the  thalamus  itself.  The 
posterior,  basal  region  of  the  interbrain  where  this  occurs  has  received  the 
name  of  regio  sulthalamica.  The  metathalamus  has  become  more  thoroughly 
understood  only  through  the  investigations  of  Luys,  Forel,  Flechsig,  Wer- 
nicke,  MonaJcow,  and  Kolliker.  Yet  we  are  still  far  distant  from  an  under- 
standing of  the  complicated  relations  which  are  presented  in  this  small 
region,  a  region  where  fibers  of  very  different  origin  meet  with  one  another, 

(271) 


272  ANATOMY   OF   THE    CENTRAL   NERVOUS    SYSTEM. 

intermingle,  and  decussate,  a  region  containing  gray  masses  which  are  them- 
selves again  filled,  in  part,  by  a  fine  net-work  of  small  decussating,  medul- 
lated  fibers. 

Fig.  175  shows  some  of  the  details  of  a  section  through  this  region.  Below  the 
thalamus  is  a  roundish  ganglion,  the  nucleus  tegmenti,  the  red  nucleus  of  the 
tegmentum ;  external  to  this  there  has  appeared  the  corpus  subthalamicum  (nucleiis 
of  Luys),  which  has  a  somewhat  lenticular  form.  Posteriorly,  the  nucleus  tegmenti 
will  appear  much  larger  in  the  transverse  sections.  It  is  the  point  of  origin  of  a 
large  bundle,  the  peduncle,  or  Tr.  tegmento-cerebellaris,  which  passes  to  the  op- 
posite half  of  the  cerebellum.  Ventral  to  it,  and  mesial  to  the  corpus  subthalamicum, 
there  is  found  a  third  ganglion,  the  substantia  nigra  Someringi,  an  accumulation  of 
nerve-cells  which  are  mostly  pigmented  with  gray.  This  is  also  better  developed  in 
the  more  posterior  planes.  It  lies  directly  over  the  fiber-systems  from  the  internal 
capsule,  which  now  become  the  pes. 

From  the  regio  subthalamica  on  down  as  far  as  the  end  of  the  midbrain  this 
dark-grayish  ganglion  may  always  be  demonstrated  above  the  pes. 

There  terminates  in  the  substantia  nigra,  designated  as  the  stratum  intermedium 
pedunculi,  the  last  remnant  of  the  fiber-system  from  the  corpus  striatum. 

Between  the  ventral  nucleus  of  the  thalamus  and  the  ganglia  men- 
tioned there  pass  a  great  many  convergent  white  fibers.  They  arise  from 
several  sources,  and  also  have  an  approximately  stratified  disposition;  so 
that  the  individual  layers  may  be  separated  somewhat.  Nevertheless,  "de- 
generation" preparations  were  the  only  ones  on  which  the  discrimination 
could  be  clearly  made.  Farthest  lateral  lie  the  tracts  of  the  tegmental  path- 
way destined  for  the  ventral,  thalamic  nucleus.  It  has  long  been  believed 
that  some  of  them  turned  directly  downward  to  the  afterbrain,  and  this 
part  was  designated  as  the  superior,  or  cortical,  fillet.  Even  now  this  view 
is  maintained  on  some  sides  (see  my  older  Fig.  168,  also).  But  in  the  last 
few  years  it  has  been  successfully  shown  that  the  fiber-tract  from  the  cortex 
terminates  in  the  thalamus,  that,  however,  a  new  pathway  arises  from  this, 
the  tractus  thalamo-bulbaris,  the  superior  fillet,  which  may  be  followed  down- 
ward as  far  as  into  the  nuclei  of  the  posterior  columns.  This  is  a  portion 
of  the  sensory  pathway,  of  which  we  now  know  two  parts:  the  cortico-thalamic 
and  the  thalamo-oblongatal  parts.  Ending  extraordinarily  near  to  one  an- 
other, both  must  be  in  intimate  contact  within  the  ventral  thalamic  nucleus 
(MonaJcow,  Mahaim,  Bielschofsky). 

The  superior,  or  upper,  fillet  is  found,  on  the  sections  illustrated,  ven- 
tral to  the  thalamus  and  near  to  the  nucleus  tegmenti.  But  it  is  separated 
from  this  by  means  of  a  thick  medullated  bundle,  the  tractus  cortico-teg- 
mentalis,  the  coronal  bundle  of  the  tegmental  nucleus  (Dejerine).  Laterally 
the  superior  fillet  and  the  coronal  bundle  form  a  true  medullary  capsule 
around  the  nucleus  tegmenti:  the  lamina  medullaris  nuclei  tegmenti. 

The  radiations  to  the  tegmental  nucleus  and  to  the  superior  fillet  do  not 


METATHALAMUS  AND  HYPOTHALAMUS. 


273 


form,  however,  the  only  elements  of  the  medulla  of  the  regio  subthalamica. 
In  the  section  from  the  dog,  shown  in  Fig.  176,  which  falls  somewhat  farther 
frontally  than  Fig.  175,  and  also  subsequently  in  Fig.  178,  you  see  large 


Fig.  176. — From  the  dog.  Frontal  section  through  about  the  middle  of  the 
thalamus.  Beneath  the  corpus  callosum  lie  the  frontal  ends  of  both  cornua 
Ammonis,  which  are  connected  by  means  of  the  psalterium,  and  send  out  the 
immense  fimbria  on  each  side.  In  the  thalamus:  the  nucleus  medialis  and 
lateralis  in  their  greatest  expanse,  separated  from  one  another  by  the  lamina 
medullaris  interna,  cut  transversely;  bounded  dorsally  by  the  taenia  thalami, 
into  which  fibers  pass  from  the  stratum  zonale,  bounded  by  the  posterior  part 
of  the  nucleus  anterior  and  the  dorso-frontal  ganglion  of  the  ganglion  habenulse. 
Lateral  and  dorsal,  the  tail  of  the  nucleus  caudatus  and  its  association-bundle. 
From  the  capsula  interna  enters  the  corona  radiata  of  the  nucleus  lateralis 
and  of  the  nucleus  anterior;  between  the  nucleus  lateralis  and  the  capsula  in- 
terna there  develops  from  the  first  the  lamina  medullaris  externa.  At  the  base, 
the  corpus  mamillare,  in  which,  at  the  level  of  this  section,  the  bundle  of  Vicq 
d'Azyr  from  the  nucleus  anterior  and  the  tegmental  bundle  enter  united.  Lat- 
erally there  develops  the  pedunculus  mamillaris;  dorsally,  directly  beneath  the 
ventricle,  the  decussatio  subthalamica  anterior.  The  capsula  interna  lies  exposed 
on  the  under  surface  as  the  pes  pedunculi;  its  most  mesial  fibers  here  arise  from 
the  forebrain-bundle  and  end  in  the  corpus  Luys.  Dorsal  to  the  corpus  Luys  the 
fibers  of  the  deep  olfactory  medulla,  and,  lying  close  to  these,  the  radiatio  thalami 
ventralis.  Lateral  to  the  capsula  interna,  the  lenticular  nucleus,  from  which  the 
ansa  lentiformis  applies  itself  closely  to  the  pes.  Between  the  ansa  and  the 
ventral  part  of  the  cornu  Ammonis,  the  nervus  opticus. 

Bas.  V.  Him  Bdl.,  basal  forebrain-bundle.     GitterscMcht,  latticed  layer. 

18 


274  ANATOMY    OF   THE    CENTRAL    NERVOUS    SYSTEM. 

fiber-masses,  arranged  in  several  bundles,  converge  toward  this  region.  They 
all  originate  from  the  corpus  striatum,  and  terminate,  so  far  as  at  present 
known,  in  the  nuclei  of  the  stratum  intermedium  (Zwischenschicht),  espe- 
cially in  the  substantia  nigra  and  in  the  corpus  subthalamicum,  or  at  least  in 
its  neighborhood,  where  there  are  found  several  other  small  ganglionic  ac- 
cumulations: the  ganglia  of  the  stratum  intermedium. 

This  radiation  is  no  other  than  the  posterior  end  of  the  tractus  strio- 
thalamici,  which  we  have  met  with  so  frequently  from  the  fishes  on  up  to 
man.  It  arises  from  the  ansa  lentiformis,  comes  to  view  at  the  mesial  bor- 
der of  the  corpus  striatum,  crosses  over  the  capsule,  and,  coming  from  the 
side,  streams  thus  into  the  separate  ganglia  of  the  stratum  intermedium. 

That  these  fiber-bundles,  designated  as  separate  strata  of  the  stratum  inter- 
medium, arise,  at  least  in  great  part,  from  the  corpus  striatum,  I  conclude  from  the 
preparations  from  the  dog  without  forebrain,  which  have  been  repeatedly  referred 
to  here. 

The  region  ventral  to  the  thalamic  ganglia  and  to  the  ansa  peduncularis 
(Fig.  169)  is  traversed  by  fine  longitudinal  fibers,  which,  arising  from  the 
olfactory  lobe,  pass  to  this  region  in  a  straight  line.  We  will  designate  them 
as  the  olfactory  bundles  of  the  interbrain.  They  may  be  traced  as  far  as  into 
the  region  of  a  ganglion-complex  which,  situated  at  the  base  of  the  inter- 
brain,  there  projects  as  a  small  hemisphere  on  the  base  of  the  skull. 

It  is  called  the  corpus  mamillare,  and  is  very  much  larger  in  the  osmatic 
vertebrates  than  in  the  Primates  (compare  Fig.  141).  In  Figs.  176  and  178 
it  falls  exactly  in  the  plane  of  section. 

Down  toward  the  corpus  mamillare  there  passes  through  the  central 
ventricular  gray  matter  the  bundle  of  the  pillar  of  the  f ornix  from  the  cornu 
Ammonis  and  the  marginal  convolution.  The  bundle  appears  to  end  in  it 
partly  on  the  same  side,  partly  on  the  opposite.  The  small  decussation 
dorsal  to  the  corpus  mamillare,  which  contains,  in  part  at  least,  fornix 
fibers,  is  called  the  anterior  decussation  of  the  regio  subthalamica.  In  Figs. 
133  and  134  trace  the  course  of  the  fornix  from  the  cornu  Ammonis  on 
down  as  far  as  the  region  just  described.  Frequently  consult  these  figures, 
also,  for  the  following  description : — 

The  corpus  candicans  consists,  as  Gudden's  experiments  showed,  of 
three  nuclei.  The  most  lateral  nucleus  sends  its  pedicle  (pedunculus  corporis 
mamillaris)  far  down  into  the  oblongata;  from  the  posterior  of  the  two 
mesial  nuclei  arises  a  thick  bundle  which  ascends  into  the  thalamus  and 
is  lost  in  its  tuberculum  anterius.  This  tractus  thalamo-mamillaris 
(bundle  of  Vicq  d'Azyr)  is  entirely  visible  in  Fig.  144,  and,  for  a  part  of 
its  course,  in  Fig.  174.  Close  beside  this,  coming  from  the  more  anterior 
nucleus,  or  ganglion,  there  ascends  a  small  fiber-strand  toward  the  thalamus. 


METATHALAMUS  AND  HYPOTHALAMUS. 


275 


It  soon  separates,  however,  from  its  companion  and,  bending  down  pos- 
teriorly at  an  angle,  extends  into  the  tegmentum,  posterior  to  the  region  of 
the  corpora  quadrigemina,  where  it  may  be  traced  until  into  the  ganglia 
that  lie  beneath  the  aquaBductus  Sylvii.  This  is  the  tegmental  bundle  of  the 
corpus  mamillare. 

8.  Ram6n  y  Cajal  and  Kolliker  have  recently  stated  that  only  a  single  bundle 
arises  from  the  corpus  mamillare,  which  passes  dorsally.  The  axis-cylinders  of  this 
bundle  divide  at  some  distance  from  their  point  of  origin.  The  anterior  branches, 
or  divisions,  ended  as  the  tractus  thalamo-mamillaris  in  the  nucleus  anterior,  the 
posterior  as  the  tegmental  bundle  in  a  nucleus  of  the  frontal  tegmentum.  Kolliker 


Fig.  177.— From  the  dog.  Frontal  section  through  the  interbrain  in  the 
region  of  the  posterior  third  of  the  thalamus.  For  the  explanation  of  the  greater 
part  of  the  figure,  see  Fig.  169.  In  comparison  with  that  of  Fig.  169  there  is 
to  be  noted  in  this  section:  the  ganglion  habenulae,  in  which  the  tsenia  dis- 
appears; the  inferior  thalamic  pedicle;  the  radiation  of  the  ansa  lentiformis 
into  the  medulla  of  the  regio  subthalamica ;  the  corpus  Luys;  and  the  separa- 
tion of  the  superior  fillet  from  the  medullary  masses  lateral  and  ventral  to  the 
thalamus.  The  pulvinar  appears  mesial  to  the  corpus  geniculatum  laterale. 
Haul).  Bd.  Mam.,  Tegmental  mamillary  bundle.  Mark  d.  Reg.  suUJialarnica, 
Medulla  of  the  regio  subthalamica.  Nucl.  H.  L.  Bdl.,  Nucleus  of  posterior  longi- 
tudinal bundle.  Obere  ttchleife,  Superior  fillet.  Pars  caudalis  Capsulce,  etc., 
Posterior  portion  of  the  capsula  interna,  principally  optic  radiation.  Stiel  d. 
Corp.  genie,  u.  Pulvinar,  Pedicle  of  the  corpus  geniculatum  and  pulvinar.  Vnt. 
Thai.  Stiel,  Inferior  thalamic  pedicle. 


276  ANATOMY   OF   THE    CENTRAL   NERVOUS    SYSTEM. 

does  not  regard  the  fornix  as  terminating  in  the  corpus  mamillare,  but  thinks  that 
after  crossing  through  the  same  it  goes,  via  the  decussatio  hypothalamica,  into  the 
opposite  thalamus,  where  it  is  said  to  end  within  the  ventral  nuclear  groups. 

By  means  of  the  substantia  nigra,  the  fiber-systems  which  pass  down- 
ward from  the  forebrain  and  interbrain  are  divided  into  two  parts,  which 
differ  as  to  their  physiological  significance,  the  pes,  or  crusta,  and  the 
tegmentum. 

Now  let  us  briefly  consider  the  glandula  pinealis  (conarium),  or 
epiphysis,  which,  with  its  pedicles  running  on  the  inner  side  of  the  thalamus, 
represents  a  portion  of  the  roof  of  the  interbrain  (see  Figs.  20  and  21). 
It  consists  essentially  of  solid  epithelial  tubules,  which  have  originated 
through  proliferation  of  the  primary  evagination. 

The  conarium  contains,  in  addition  to  the  tubules  and  an  abundant 
blood-supply,  the  brain-sand:  small  concretions  of  a  stratified  structure, 
which  consist  principally  of  calcium-salts  and  of  a  small  organic  basis. 

The  position  of  the  glandula  pinealis,  at  the  posterior  end  of  the  thala- 
mus and  between  the  corpora  quadrigemina,  is  shown  in  Fig.  125. 

I  would  like  to  remind  you  again  of  what  was  said  on  page  127  about 
the  significance  of  the  conarium  in  reptiles. 

Fibers  appear  to  extend  as  far  as  the  conarium  from  the  tracts  of  the  tsenia 
thalami.  The  tsenia  rises  anteriorly  by  the  side  of  the  fornix  from  the  depth  of  the 
olfactory  field  and,  after  it  has  received  an  afferent  tract  from  the'  fornix,  ends  in 
the  ganglion  habenulce  after  it  has  passed  along  the  mesial  edge  of  the  thalamus. 
The  ganglion  is  located  just  in  front  of  the  epiphysis  (see  Fig.  177).  The  posterior 
portion  of  the  bundles  of  the  taenia  is  also  designated  as  the  pedunculi  conarii. 
Between  the  two  pedunculi  conarii  runs  the  delicate  commissura  habenularis,  prob- 
ably a  decussating  tract  from  the  tseniae  habenulae  (very  clearly  shown  in  transverse 
section  in  Fig.  144).  It  is  also  to  be  noted  in  Fig.  144  how  the  glandula  pinealis, 
almost  massive  in  man,  appears  in  the  rabbit  to  be  an  evagination  of  the  roof  of  the 
forebrain  and  passes  over  into  the  plexus  chorioideus. 

Precisely  as  in  the  lower  vertebrates,  so  in  mammals,  a  large  tract  passes  down 
to  the  base  of  the  midbrain  from  the  ganglion  habenulse.  It  is  the  tractus  liabenulo- 
peduncularis. 

I  will  now  take  up  again  the  demonstration  of  the  brain-sections  that 
was  interrupted  at  the  close  of  the  last  chapter.  They  are  intended  to  assist 
you  in  reviewing  and  studying  what  has  just  been  presented,  and  to  serve 
as  a  means  of  orientation.  The  section  shown  in  Fig.  178  follows  directly 
upon  that  of  Fig.  174. 

Located  just  behind  the  chiasma,  the  section  shows,  on  the  one  hand,  the 
thalamus  in  its  greatest  breadth;  on  the  other,  as  an  important  factor,  the  emerging 
of  the  fiber-systems  of  the  internal  capsule  at  the  base  of  the  brain  as  the  fundament 
of  the  pes,  or  crusta.  Between  the  pes  and  the  thalamus  is  situated  the  regio  subtha- 
lamica,  and  new  ganglia  lie  in  this.  Note  the  "ganglion  of  the  zona  incerta,"  the 
corpus  subthalamicum  (Luys),  and  ventrally  the  group  of  ganglia  of  the  corpus 


METATHALAMUS    AND    HYPOTHALAMUS. 


277 


mamillare.  The  latter  is  surrounded  by  its  medullary  capsule,  in  which  the  fornix 
has  now  disappeared,  and  it  sends  away  above  the  tegmental  bundle  (the  tractus 
maimllo-tegmentalis),  and  the  tractus  thalamo-mamillaris  (the  bundle  of  Vicq 
d'Azyr).  which  at  first  pass  along  united. 

The  nucleus  lateralis  and  medialis  thalami  allow  the  posterior  end  of  the  nucleua 
anterior  to  extend  between  them  dorsally;  ventrally  they  flow  together.  Here 
begins  the  region  of  the  nucleus  ventralis.  The  more  posterior  portion  of  the  ansa 
lentiformis  streams  in  here,  and  other  fibers  from  the  corpus  striatum  go  to  the  gray 


Nncl.  an 
Lam.  med 
Tr.  thai 

Corp.  call os 
Nucl.  lat 


Lob.  temper. 


Fig.  178. 


nuclei  of  the  regio  subthalamica.  The  lamina  medullaris  interna  thalami  has  become 
much  richer  in  fibers,  and  between  the  latticed  layer  and  the  lateral  nucleus  there 
develop  the  tracts  of  the  lamina  medullaris  externa  thalami.  The  stratum  zonale 
is  very  perceptibly  diminished,  and  the  toenia  is  to  be  seen  more  clearly.  The 
lenticular  nucleus,  the  claustrum,  the  capsulae,  and  the  cortex  of  the  insula,  with  the 
exception  of  somewhat  altered  forms,  present  nothing  that  differs  essentially  from 
the  sections  previously  shown.  In  the  white  medullary  substance  the  long  asso- 
ciation-tracts may  still  be  sought  for  in  the  same  situations  where  they  lay  in  the 
section  shown  in  Fig.  174. 


278 


AXATOMY    OF    THE    CENTRAL   NERVOUS    SYSTEM. 


Posterior  to  the  region  of  the  previous  section,  the  separate  elements  found  in 
the  regio  subthalamica  and  in  the  tegmentum,  which  is  here  increasing,  lie  so  closely 
upon  one  another  that,  for  the  most  part,  they  are  not  separable  without  staining 
and  magnification.  In  the  illustrations  found  farther  front  in  the  text,  much  will, 
therefore,  be  clearer  than  in  Fig.  179;  see  especially  the  figures  from  the  dog. 

The  thalamic  ganglia  are  almost  entirely  blended  together.  Only  the  form  of 
the  cells  and  degenerative  changes  now  allow  the  separation  of  special  nuclei.  The 
nucleus  lateralis  and  the  nucleus  ventralis  have  gained  the  most  in  expanse;  the 
mesial  and  the  anterior  nucleus  have  entirely  disappeared.  Here,  close  to  the  en- 
trance into  the  aqueduct,  the  layer  of  central,  ventricular  gray  matter  increases  in 
thickness  also.  Just  outside  of  it  appear  the  "sagittal  nuclei  of  the  interbrain": 
the  nuclei  of  the  posterior  longitudinal  bundle.  Then  follows  laterally  the  red,  teg- 
mental  nucleus,  and,  in  the  place  where  the  corpus  subthalamicum  was  situated  in 
the  last  section,  the  substantia  nigra.  The  first-named  ganglion  has  dwindled  to  a 


Corpus  callus 


Fig.  179. — Section  through  the  regio  subthalamica. 


small  remnant  which  lies  farther  laterally.  In  the  clear  field  ventral  to  the  thal- 
amus  there  are  gathered:  fibers  from  the  most  posterior  territory  of  the  fiber-sys- 
tems of  the  corpus  striatum,  forming  a  capsule  around  the  red  nucleus  and  entering 
into  it  in  part;  then  fibers  of  the  tracts  of  the  lamina  medullaris  externa;  and, 
separated  from  this  by  gray  matter,  in  the  most  ventral  thalamic  nucleus,  the  fibers 
of  the  superior  fillet.  The  internal  capsule  contains,  in  this  situation,  substantially 
the  tegmental  radiation  to  the  thalamus  and  tracts  from  the  posterior  region  of  the 
temporal  lobe  to  the  thalamus,  also  tracts  from  the  same  source  to  the  pes  pedun- 
culi— that  is,  to  its  lateral  portion. 

Ventral  to  the  putamen,  here  considerably  diminished,  there  is  recognized  the 
radiation  of  the  commissura  anterior  in  the  neighborhood  of  the  inferior  horn.  Into 
the  inferior  horn  itself  the  most  anterior  part  of  the  cornu  Ammonis  is  now  seen 
to  infold  and  project.  The  roof  of  the  inferior  horn  here  also  contains  the  tail  of 
the  nucleus  caudatus,  which  is  curved  downward,  and  then,  naturally,  the  fiber- 


METATHALAMUS   AND    HYPOTHALAMUS.  279 

system  from  the  temporal  lobe  to  the  thalamus.  Outside  the  ventricle,  and  separated 
from  this  by  the  plexus  chorioideus,  lies  the  tractus  opticus.  The  pes  pedunculi  is 
separated  from  that  of  the  opposite  side  by  the  substantia  perforata  posterior. 

The  two  columns  of  the  fornix  are  united,  and  form  a  short,  thin  plate  already 
in  relation  with  the  psalterium. 


CHAPTEE    XVIII. 

THE  BASE  or  THE  BKAIN.     THE  OPTIC  NERVE  AND  ITS  ORIGIN. 
THE  CORPORA  QUADRIGEMINA. 

WE  have  hitherto  taken  no  occasion  to  examine  the  base  of  the  brain 
more  thoroughly.  Now,  when  the  origin  of  several  of  the  structures  found 
there  is  known  to  us,  it  may  be  time  gently  to  free  a  brain,  with  the  base 
turned  upward,  from  the  pia  and  blood-vessels,  and  to  study  the  preparation 
so  made. 

The  illustration  that  follows  may  serve  as  a  guide.  First  of  all,  the 
crura  cerebri  are  seen  to  emerge  from  out  the  mass  of  the  cerebrum.  Just 
in  front  of  them,  in  the  space  here  concealed  for  the  greater  part  by  the 
optic  nerve,  lies  the  substantia  innominata,  which  contains  the  ansa  lenti- 
formis  and  the  inferior  thalamic  pedicle  (see  Fig.  174  also).  Frontal  sec- 
tions, previously  demonstrated,  have  taught  you  that  the  white  mass  here 
visible,  the  pes,  is  the  direct  continuation  of  the  fibers  of  the  internal  cap- 
sule. After  a  short  course  the  crus  cerebri  is  covered  by  thick  masses  of 
fibers,  which  appear  to  pass  transversely  across  it  from  one-half  of  the  cere- 
bellum to  the  other.  These  fibers  are  designated  as  the  pontal  fibers,  or  fibres 
pontis.  On  the  other  side  of  the  pons  a  part  of  the  fibers  contained  in  the 
pes  pedunculi  can  again  be  seen  as  the  pyramids,  another  part  has  termi- 
nated in  the  ganglia  that  are  scattered  in  between  the  fibers  of  the  pons. 

The  gray  matter  between  the  crura  cerebri  is  called  the  substantia  per- 
forata  posterior.  It  borders  internally  on  the  regio  subthalamica.  In  front 
of  it  lie  the  corpora  mamillaria,  those  two  roundish  ganglia  that  we  have 
previously  met  with  in  transverse  section:  the  same  ganglia  to  which  the 
bundle  of  Vicq  d'Azyr  passes  from  the  thalamus,  the  ganglia  in  which 
the  fornix  ends. 

In  front  of  the  corpora  mamillaria  the  floor  of  the  middle  ventricle, 
which  is  here  designated  as  the  tuber  cinereum,  bends,  or  bulges,  downward 
and  forward — so  that  a  funnel  arises,  the  lumen  of  which  is  nothing  but.  the 
continuation  of  the  ventricle.  At  the  lower,  pointed  end  of  this  funnel,  the 
infundibulum,  the  hypophysis  is  attached  (see  Fig.  162). 

The  hypophysis— an  appendix  to  the  base  of  the  brain,  about  the  size  of  a 
cherry — consists  first  of  all  of  the  continuation  of  the  ventricular  floor,  the  lobus 
infundibuli,  or  lobus  posterior,  which  is  not  positively  known  to  be  of  a  nervous 
nature.  In  front  of  this  lies  the  anterior  lobe,  a  tuft  of  epithelial  tubules,  which  has 
grown  firmly  to  the  lobus  infundibuli,  and  which,  as  you  know,  arises  from  the 

(280) 


BASE    OF   BRAIN,    OPTIC    NERVE,   AND    CORPORA   QUADRIGEMINA.       281 

mucous  membrane  of  the  pharynx.  Recent  investigations  (Flesch,  Dostojewsky) 
make  possible  the  recognition  of  two  kinds  of  cells  in  it:  smaller,  clear  cells,  and 
larger,  granular,  and  cloudy  cells.  Since,  as  is  known,  exactly  similar  elements  are 
found  in  several  very  active  glands,  it  is  thus  probable  that  the  hypophysis  also  per- 
forms some  physiological  function.  The  hyperplasia  of  the  epithelial  part  hitherto 


Fig.  180. — The  base  of  the  brain;  the  left  lobus  temporali.s  is,  in  part,  rep- 
resented as  transparent  in  order  that  the  entire  course  of  the  tractus  opticus 
might  be  seen. 


established  in  several  cases  of  myxcedema  points  directly  thereto.  Between  the 
pharyngeal  and  the  cerebral  lobes  of  the  hypophysis  there  is  found  a  number  of 
other  epithelial  tubules,  the  lumina  of  which,  as  far  as  I  can  ascertain,  are  not  con- 


282  AXATOHY    OF    THE    CENTRAL    NERVOUS    SYSTEM. 

nected  with  either  the  one  or  the  other  part  of  the  hypophysis.  The  accompanying 
sagittal  section  through  the  hypophysis  of  a  human  embryo  of  four  months  shows  all 
three  parts  very  plainly. 

The  optic  tracts  pass  in  a  broad  curve  around  the  infundibulum  and 
over  the  peduncles  in  a  direction  toward  the  pulvinar  of  the  thalamus. 
Concealed  on  both  sides  by  the  lobus  temporalis,  they  curve  upward  and 
outward  around  the  origin  of  the  peduncles,  the  crura  cerebri,  to  attain  the 
corpus  geniculatum  laterale  and  the  pulvinar. 

Anteriorly,  in  front  of  the  infundibulum,  the  tracts  unite  to  form  the 
chiasma,  from  which,  after  the  decussation  of  a  part  of  their  bundles,  the 
optic  nerves  proceed. 

In  front  of  the  optic  tract  and  lateral  to  the  chiasma  there  lies,  just 
under  (above,  when  examining  the  brain  from  the  base)  the  anterior  part 
of  the  corpus  striatum,  the  substantia  perforata  anterior,  a  gray  mass  that 


Cr  an  ium. 

Fig.    181. — Sagittal    section    through    the   brain-floor    and    the   hypophysis    of    a 
human  embryo  of  four  months.     Combined  from  three  consecutive  sections. 


is  pierced  by  numerous  vessels  from  the  pia.    The  region  of  the  lobus  olfac- 
torius  begins  in  front  of  it. 

The  substantia  perforata  anterior  is  nothing  else  but  the  olfactory  field, 
or  area,  which  has  become  greatly  atrophied  in  man.  In  Primates  the  lobus 
olfactorius  is  also  atrophied  along  with  the  entire  olfactory  apparatus.  In 
man  only  the  most  posterior  part  of  it  has  been  retained  with  its  cortical 
structure  (Figs.  172  and  173);  the  anterior  part  has  diminished  to  an  insig- 
nificant, gray  cord,  the  tractus  olfactorius,  on  which  anteriorly  is  found  the 
small  bulbus  olfactorius.  From  the  bulbus,  however,  there  still  arise,  pre- 
cisely as  in  the  other  vertebrates,  the  large  fiber-tracts  of  the  olfactory  radi- 
ation. Since  these  pass  backward  to  the  cortex  of  the  lobulus  olfactorius 
and  the  region  of  the  gyrus  hippocampi,  they  must  pass  over  the  tractus 
olfactorius,  giving  a  white  appearance  to  its  under  side.  After  reaching 
the  olfactory  field  (the  substantia  perforata  anterior)  the  tracts,  which  here, 


BASE    OF    BRAIN,    OPTIC    NERVE,    AND    CORPORA    QUADRIGEMINA.        283 

to  be  sure,  are  essentially  thinner,  split  up  exactly  as  they  do  in  the  osmatic 
vertebrates,  and  pass  away  as  white  strands — earlier  named  olfactory  roots — 
over  the  gray  substance.  A  lateral  tract,  often  divided  into  two,  may  com- 
monly be  separated  from  a  mesial.  The  former  gradually  turns  inward 
near  to  the  gyms  hippocampi.  At  times  a  thin,  light-colored  cross-band 
may  be  seen  to  pass  over  the  substantia  perforata  anterior  from  without 
inward  and  upward.  It  is  nothing  other  than  the  atrophied  remnant  of 
the  olfactory  bundle  to  the  cornu  Ammonis,  which  is  to  be  seen  in  so 
high  perfection  in  this  situation  in  the  osmatic  vertebrates.  Before  leaving 
the  consideration  of  the  base  of  the  brain,  turn  once  more  to  Fig.  144,  be- 
cause in  the  osmatic  brain  there  shown  so  many  relations  appear  clearer; 
and  the  structures  are  better  developed.  The  olfactory  apparatus,  especially, 
will  then  be  clearer  to  you. 

On  the  mesial  edge  of  the  substantia  perforata  anterior  the  fibers  of  the 
corpus  callosum  dip  down  as  far  as  the  base  of  the  brain.  The  elevation  they 
here  produce  on  the  inner,  mesial  cortex  of  the  hemisphere,  extending  nearly 
to  the  base  of  the  brain,  is  designated  as  the  gyrus  subcallosus.  Between 
the  two  gyri  subcallosi  there  lies  a  gray  plate,  which  may  be  traced 
upward  as  far  as  the  genu  of  the  corpus  callosum.  It  is  the  lamina  ter- 
minalis.  In  it  we  must  recognize  a  remnant  of  the  embryonic  closing  plate 
— that  wall  which  once  closed  in  the  primary  forebrain,  the  same  wall  from 
which  the  hemispheres,  now  of  such  enormous  size,  grew  and  arched  over 
the  other  parts  of  the  brain.  Now,  this  is  only  a  small  gray  area  of  little 
importance,  which  lies  at  the  most  anterior  point  of  the  base  of  the  brain 
(Fig.  133). 

If  an  affection  involves  only  the  base  of  the  brain  in  front  of  the  pons,  the 
symptoms  that  are  produced  by  irritation  or  paralysis  of  the  nerves  lying  there  will 
be,  by  far,  the  most  important  for  diagnosis.  Moreover,  disturbances  of  motility  and 
sensibility  may  also  appear  in  the  extremities  if  the  crura  cerebri  are  involved  with 
the  rest.  A  careful  analysis  of  the  symptoms  with  the  aid  of  an  illustration  of  the 
base  of  the  brain  often  leads  to  a  surprisingly  accurate  diagnosis  of  the  location  of 
the  lesion. 

The  optic  tracts  curve  around  the  crura  cerebri  and  disappear  farther 
dorsally  in  the  region  of  the  corpora  quadrigemina,  particularly  in  a  small 
ganglion  lying  adjacent  to  this  laterally,  the  corpus  geniculatum  laterale. 
If  you  now  wish  to  become  better  acquainted  with  the  actual  termination 
of  the  optic  nerves,  you  must  first  of  all  give  your  attention  to  those  parts 
of  the  midbrain  just  mentioned. 

The  following  illustration  shows  the  corpora  quadrigemina  when  seen 
from  above.  They  lie  upon  the  peduncles,  somewhat  crowded  in  between 
the  thalami.  Behind  them,  on  each  side,  a  large  fiber-tract  comes  from  be- 
neath them  and  sinks  into  the  cerebellum.  It  is  the  anterior  cerebellar 


284 


ANATOMY    OF   THE    CENTKAL    NEKVOUS    SYSTEM. 


peduncle.    It  arises  from  the  nucleus  ruber  tegmenti,  which  lies  in  the  teg- 
mentum  beneath  the  thalamus  and  the  corpora  quadrigemina. 

We  distinguish  anterior  and  posterior  corpora  quadrigemina,  but  this 
distinction  is  easy  to  the  naked  eye  in  many  mammals  alone.    In  all  other 


Fig.  182.  —  The  brain-structures  from  the  thalamus  to  the  spinal  cord  (the 
"brain-stem").  The  cerebellum  divided,  and  removed  on  the  left.  Bindearm, 
Peduncle.  Hinterhirn,  Hindbrain.  Hirnschenkel,  Crus  Cerebri.  Kleinhirn,  Cere- 
bellum. Mittelhirn,  Midbrain.  Nachhirn,  After-brain.  Riickenmark,  Spinal  cord. 
Zwischenhirn,  Interbrain. 


vertebrates  the  anterior  are  so  large  that  the  posterior  corpora  quadrigemina 
disappear  as  small  ganglia  in  the  region  under  them.  From  the  anterior 
corpora  quadrigemina  arises  a  part  of  the  optic  nerves.  The  anterior  cor- 


BASE    OF   BRAIN,    OPTIC   NERVE,,    AND    CORPORA    QUADRIGEMINA.       285 

pora,  like  the  thalami,  receive  fibers  from  the  territory  of  the  occipital  lobe, 
which  run  to  the  internal  capsule  in  the  optic  radiation,  and  from  there 
ascend  to  the  corpora  as  the  brachia  of  the  anterior  corpora  quadrigemina. 
Fibers  to  the  optic  tract  itself  also  run  downward  in  this  very  brachium,  or 
arm. 

The  brachium  of  the  anterior  corpus  quadrigeminum,  which  is  com- 
posed, therefore,  of  fibers  from  the  cortex  and  fibers  passing  to  the  optic 
tract,  sends  its  cortical  fibers  alone  into  the  corpus  quadrigeminum;  its 
optic-nerve  fibers  spread  out  over  the  gray  surface  of  the  quadrigeminal 
body,  thus  forming  the  stratum  zonale,  and  there  sink  below. 

The  posterior  corpus  quadrigeminum  appears,  at  first  sight,  it  is  true, 
to  stand  in  some  relation  with  the  optic  tract,  but  it  is  very  improbable  that 
it  contains  fibers  which  are  used  in  the  visual  act.  Its  brachium  arises  from 
the  corpus  geniculatum  mediale  and  also  from  the  commissura  inferior  (Gud- 
den's  commissure),  not  previously  mentioned,  which  passes  along  with  the 
optic  tract  to  the  posterior  angle  of  the  chiasma. 

The  posterior  quadrigeminal  body  receives  its  coronal  fibers  (MonaTcow)  from 
the  lobus  temporalis.  The  extraordinary  development  of  the  posterior  corpus  quad- 
rigeminum in  whales,  and  the  huge  tracts  which,  in  these  vertebrates,  pass  from 
there  to  the  acusticus  nucleus  of  the  opposite  side  make  it  probable  (Spitzka)  that 
this  ganglion  stands  in  some  relation  with  the  auditory  nerve.  The  results  of  ex- 
perimental investigations,  directed  thereto,  are  in  accord  with  this  view.  After  de- 
struction of  the  auditory-nerve  nuclei,  the  secondary  fiber-systems  of  the  same 
atrophy  as  far  as  the  posterior  corpora  quadrigemina  (BaginsTty,  Bumm). 

When  seen  from  the  side,  the  relations  of  the  quadrigeminal  brachia 
to  the  ganglia  and  the  tractus  opticus  are  very  clear;  likewise  the  rela- 
tions of  the  corpora  geniculata:  the  corpus  geniculatum  mediale,  lying  ad- 
jacent to  the  posterior  brachium;  the  corpus  geniculatum  laterale,  appearing 
to  be  thrust  in  between  the  pulvinar  and  the  tractus  opticus,  of  which 
mention  was  made  when  the  thalamus  was  described. 

The  tractus  opticus  receives  fibers  from  the  latter  ganglion,  in  addition 
to  fibers  from  the  pulvinar  thalami  and  its  stratum  zonale. 

The  opticus  fibers  from  the  anterior  corpora  quadrigemina  were  men- 
tioned previously.  They  probably  run,  for  the  greater  part,  in  the  brachium 
of  the  anterior  corpus  quadrigeminum. 

In  the  lower  vertebrates  the  optic  nerve  arises  mostly  from  the  anterior  corpora 
quadrigemina;  the  other  centers  of  origin,  on  the  other  hand,  are  very  insignificant. 
The  greater  the  development  of  the  occipital  cortex,  however, — the  cortex  which 
sends  its  fiber-systems  principally  into  the  other  centers,  or  terminals,  and  only 
supplies  the  anterior  corpora  quadrigemina  with  a  relatively  insignificant  afferent 
tract, — the  more  do  the  fibers  of  the  optic  nerves  arise  from  these  terminals,  and  the 
less  from  the  anterior  quadrigeminal  bodies.  This  still  continues  in  the  mammalian 


286 


ANATOMY    OF   THE    CENTRAL    NERVOUS    SYSTEM. 


series.  The  portion  of  the  opticus  arising  from  the  anterior  corpus  quadrigeminum, 
still  very  large  in  the  rabbit,  is  considerably  atrophied  in  man.  On  the  other  hand, 
the  principal  part  of  the  optic  nerve  arises  in  man  from  the  corpus  geniculatum 
laterale. 

It  may  be  expressed  as  follows:  Vertebrates  which  are  dependent  entirely,  or 
almost  entirely,  for  vision  upon  the  primary  centers,  or  terminals,  have  a  prepon- 
derating development  of  the  quadrigeminal  branch  of  the  optic  nerve.  As  soon  as 
cortical  vision  becomes  more  developed,  however,  the  centers  standing  in  more  inti- 


Fig.  183.- — Thalamus  and  corpora  quadrigemina  seen  from  the  side.  The 
forebrain  removed  at  the  point  where  its  coronal  fibers  pass  into  the  capsula 
interna.  The  relations  of  the  optic  radiation  to  the  posterior  part  of  the  capsula 
interna  and  to  the  point  of  origin  of  the  opticus  are  shown  diagrammatically. 
Bindearm,  Peduncle.  Fuss,  Pes,  or  crusta.  Hint.  Arm.,  Posterior  brachium. 
Stabkranz  zu  den  Optic  Centr.,  Coronal  fibers  to  the  optic  centers.  V.  Arm., 
Anterior  brachium. 


mate  relation  with  the  cortex — the  pulvinar,  the  corpus  geniculatum  laterale — 
become  more  important,  and  the  quadrigeminal  portion  of  the  opticus  diminishes 
relatively. 

So  much  for  the  origin  of  the  optic  nerve  as  represented  by  a  preparation  of 


BASE    OF    BRAIN,    OPTIC    NERVE,   AND    CORPORA    QUADRIGEJIINA.       287 

the  adult  human  brain.  According  to  J.  Stilling,  there  is  added  still  another  root 
which  ascends  in  the  pes  pedunculi  from  the  medulla  oblongata. 

However,  it  is  so  difficult  correctly  to  locate  and  trace  out  all  these  fibers  and 
nuclei  in  man  that  we  must  ask  ourselves  the  question:  How  far  are  the  relations 
under  discussion  supported  by  investigations  on  other  vertebrates?  First  of  all, 
comparative  anatomy  presents  us  optic  centers  of  such  magnitude  in  the  midbrain 
of  fishes  and  birds  that  the  relations  may  be  studied  there  much  more  easily  than  in 
mammals.  But  in  the  reptiles  and  amphibians,  as  well  as  in  fishes  and  birds,  it  i8 
easily  recognized  that  the  principal  part  of  the  optic  nerve  certainly  ends  in  the 
anterior  corpus  quadrigeminum,  and  that  in  its  course  past  the  corpus  geniculatum 
laterale  it  sends  numerous  collaterals  into  this  ganglion.  Experimental  investiga- 
tions (Gudden,  Ganser,  Monakow)  on  mammals  show  that  after  the  early  extirpa- 
tion of  an  eye  the  anterior  corpus  quadrigeminum,  certain  layers  of  the  corpus  gen- 
iculatum laterale,  and  fibers  from  the  pulvinar  degenerate.  The  pulvinar  is,  more- 
over, very  small  in  most  mammals,  and  first  attains  a  considerable  size  in  the 
Primates. 

It  is  already  evident  from  the  foregoing  that  numerous  methods  of  investiga- 
tion have  been  made  use  of  in  order  to  ascertain  the  course  and  termination  of  the 
fiber-system  of  the  optic  nerve.  I  have  purposely  communicated  this  to  you  some- 
what more  thoroughly  because  the  history  of  our  knowledge  here  shows  how  much 
is  to  be  gained  by  the  application  of  many  methods  to  a  single  object;  and,  more- 
over, because  I  still  have  something  to  say  concerning  new  advances  which,  accruing 
from  the  purposive  application  of  the  method  of  degeneration  and  supported  by  the 
results  of  embryological  research,  give  very  important  information  concerning  the 
combination,  and  the  histology  of  the  termination, 'of  the  optic-nerve  fibers. 

As  you  know,  only  those  fibers  degenerate  which  are  separated  from  the  cells 
from  which  they  originate.  According  as  the  optic  nerve  is  destroyed  at  its  eye  (or 
peripheral)  end  or  is  injured  at  its  terminal  points  (or  centers)  very  different  types  of 
degeneration  are  obtained.  The  study  of  such  varied  preparations  has  led  Monakow 
to  the  conclusion  that  the  majority  of  the  fibers  of  the  optic  nerve  do  not  originate 
from  the  cells  of  the  brain  at  all,  but  from  the  large  gangl  ionic  cells  of  the  retina. 
The  neuraxons  that  arise  there  pass  backward  in  the  opticus,  and  in  man  end  for 
the  most  part  in  the  corpus  geniculatum  laterale  and  in  the  pulvinar — probably  in 
a  brush-like  arborization  around  the  cells  situated  there.  The  white  lines  which 
traverse  the  gray  matter  of  the  lateral  geniculate  body  consist,  in  part,  of  such 
fibers  which  come  directly  from  the  retina.  In  fact,  P.  and  S.  Ramdn  y  Cajal  have 
been  able  to  show  such  brush-like  arborizations  of  the  optic  fibers  terminating  around 
cells  in  the  roof  of  the  midbrain  and  around  cells  in  the  corpus  geniculatum  laterale, 
for  vertebrates  of  all  classes  (see  Figs.  66  and  81  also). 

There  are  fibers,  however,  in  the  opticus  which  originate  from  the  train. 
From  the  cells  that  lie  in  the  superficial  gray  layer  of  the  anterior  corpora  quad- 
rigemina  optic  fibers  certainly  arise  in  the  rabbit  and  cat,  and  very  probably  in  man, 
which  then  go  to  the  retina,  and  there  probably  terminate  in  an  arborization  around 
the  cells  of  the  granular  layer.  The  optic  nerve  contains  fibers,  therefore,  which  arise 
from  the  retina  and  others  that  arise  from  the  primary  optic  centers.  Embryo- 
logical  studies  by  Keibel  and  His  have  shown  that  certain  of  the  optic  fibers  grow 
toward  the  brain  from  the  large  cells  of  the  retina. 

While  the  existence  of  the  opticus  roots  asserted  to  come  from  the 
corpus  subthalamicum  and  from  the  crus  cerebri  has  not  as  yet  been  suffi- 


288 


ANATOMY    OF   THE    CENTRAL    NERVOUS    SYSTEM. 


ciently  confirmed  by  the  various  methods  of  investigation,  we  may  prob- 
ably at  present  regard  it  as  firmly  established  that  optic-nerve  fibers  arise 
and  terminate  in  the  corpus  geniculatum  laterale,  in  the  superficial  medulla 
of  the  anterior  corpus  quadrigeminum,  and  in  the  outermost  layers  of  the 
pulvinar.  These  last-named  gray  masses  are  designated  as  the  primary 
optic  centers. 

A  connection  between  these  centers  and  the  cortex  of  the  occipital  lobe  has 
been  proved  in  a  definite  and  satisfactory  manner.  The  fibers  concerned  in 
this  form  the  radiatio  thalamo-occipitalis,  the  optic  radiation,  or  the  bundle 
of  Gratiolet:  a  not  inconsiderable  fiber-tract  which  develops  from  the  pri- 
mary centers  in  separate  bundles  and  passes  backward  from  there  to  become 
lost  in  the  cortex  of  the  cuneus  and  in  about  the  region  of  the  second  and 
third  occipital  gyrus. 

In  the  territory  from  which  they  originate  (the  cortex)  and  along  the 


Fig.  184. — Section  through  the  corpus  geniculatum  laterale  of  the  cat. 
Silver  method.  Shows  the  entering  optic  fibers  and  the  splitting-up  of  the  same 
into  terminal,  brush-like  arborizations.  (After  P.  Ramon  y  Cajal.) 


proximal  part  of  their  course  while  passing  away  from  there,  the  coronal 
fibers  to  the  separate  optic  centers  (or  terminals)  are  to  be  separated  from 
one  another  only  with  difficulty.  Farther  anteriorly,  however,  it  is  recog- 
nized that  the  fibers  to  the  pulvinar  occupy  the  dorsal,  and  the  fibers  to  the 
geniculatum  laterale  the  ventral,  portion  of  the  tract.  Only  in  the  most 
posterior  division  of  the  internal  capsule,  just  before  the  entrance  into  the 
primary  centers  (Fig.  165),  are  the  separate  parts  of  the  optic  radiation 
sharply  separated  from  one  another.  The  pedicle  to  the  corpus  geniculatum 
lies  close  to  this  as  the  lateral  medullary  field,  or  area.  It  arises  from  the 
cuneus,  perhaps  from  the  lobus  lingualis  also.  Dorsal  to  it,  the  fibers  of 
the  optic  radiation  arising  from  the  two  occipital  gyri  enter  the  pulvinar. 


BASE    OF    BRAIN,    OPTIC    NERVE,   AND    CORPORA    QUADRIGEMINA.       289 

Farther  dorsal  to  these  are  situated  tracts  that  become  lost  in  the  latticed 
layer  of  the  thalamus. 

These  relations  of  the  central  optic  pathway  may  be  plainly  recog- 
nized in  a  frontal  section,  passing  through  the  most  anterior  part  of  the  cor- 
pora quadrigemina. 

As  I  have  as  yet  demonstrated  no  section  from  the  midbrain  region,  Fig.  185 — 
which  is  an  addition  to  the  human  brain-sections  demonstrated  earlier — needs  a  few 
words  of  explanation. 


/  r 


'asc.  occip.-front. 
caudat. 


-Nucl.  caudatus 
... .Comm.  ant. 
...jCornu  Ammonis 


Fig.  185. — Frontal  section  through  the  forebrain  and  the  interbrain  near  the 
place  where  fibers  of  the  capsula  interna  become  the  pes,  or  crusta,  of  the  cms 
cerebri. 


The  ventricle,  which  farther  anteriorly  was  closed  in  dorsally  by  the  epithelium 
of  the  plexus  alone,  has  narrowed  here  in  the  territory  of  the  mesencephalon  to  the 
aquaeductus  Sylvii.  Over  this  the  anterior  corpora  quadrigemina  lie  like  a  roof. 
Since  these  project,  as  Fig.  125  shows,  somewhat  forward  between  the  posterior  ends 
of  the  thalami,  the  most  posterior,  thalamic  ganglia — those  of  the  pulvinar — are 
accordingly  cut  on  each  side  of  the  corpora  quadrigemina.  This  division  of  the 
thalamus  attains  its  greatest  expansion  exactly  at  the  plane  of  this  section.  Under 


290 


ANATOMY    OF    THE    CENTRAL    NERVOUS    SYSTEM. 


it  there  is  met,  as  a  glance  at  Fig.  183  shows,  the  corpus  geniculatum  laterale  and 
the  corpus  geniculatum  mediale. 

The  geniculatum  mediale  lies  in  a  direct  line  with  the  nucleus  ventralis  thai- 
ami.  Toward  the  median  line  it  has  the  fiber-systems  of  the  fillet,  with  which,  in 
these  planes,  are  now  associated  fibers  from  the  roof  of  the  midbrain. 

In  the  ventral  territory  of  the  geniculatum  laterale  the  tractus  opticus  becomes 
almost  entirely  lost,  with  the  exception  of  single  bundles  that  pass  over  the  genic- 
ulatum mediale  to  the  stratum  zonale  of  the  corpora  quadrigemina. 

The  pes  pedunculi  and  the  tegmentum  are  now  fully  developed.  They  will  be 
more  thoroughly  described  in  the  next  chapter. 


Fissura  cent.   - 


Fiss.    inter- 
pariet. 


Gynis  lin- ', 
gualis     / 


Fig.  186. 


In  this  plane  all  three  nuclei  receive  their  afferent  fibers  from  the  corona 
radiata.  The  optic  radiation,  radiatio  thalamo-occipitalis,  and  the  pathway  from 
the  temporal  lobe  to  the  geniculatum  mediale,  which  was  designated  as  the  pedicle 
(Stiel)  of  the  same  in  a  previous  illustration,  are  now  plainly  visible. 

In  its  dorsal  region  the  white  medullary  substance  principally  contains  fibers 
of  the  corpus  callosum  and  short  association-fibers.  Of  the  long  pathways,  the  fas- 
ciculus arcuatus  can,  perhaps,  be  traced  here.  In  its  ventral  half  the  white  matter 
consists  principally  of  the  fiber-systems  that  arise  from  the  occipital  lobe,  which  are 
either  fibers  belonging  to  this  lobe  itself  or  coronal  fibers  to  the  thalamus  and  to  the 
lateral  bundle  of  the  pes.  At  about  one-fourth  the  distance  from  the  base  of  the 
section  lies  the  radiatio  occipito-temporalis,  or  fasciculus  longitudinalis  inferior. 


BASE    OF   BRAIN,    OPTIC   NERVE,    AND   CORPORA    QUADRIGEMINA.       291 

The  crura  of  the  fornix  are  now  no  longer  seen,  but  there  lies  under  the  corpus 
callosum  the  broad  plate  of  the  psalterium,  on  the  edges  of  which  lie  the  fimbrise. 
Through  an  interchange  of  fibers  in  this  territory  arise  the  true  fornix  columns.  Far 
below  is  to  be  noted  the  origin  of  the  fimbria  from  the  medullary  substance  of  the 
hippocampal  cortex,  and  its  relation  to  the  inferior  horn  of  the  ventricle. 

We  will  now  at  once  trace  the  optic  radiation  farther  backward  until 
within  the  apex  of  the  occipital  lobe,  so  that  a  clear  idea  may  be  gained  of 


fLob.  pariet. 

i     sup. 


iss.    inter- 
pariet. 


w 


it  as  a  whole.    For  this  reason  I  here  demonstrate  a  section  in  Fig.  186  that 
is  located  about  three-fourths  of  a  centimeter  behind  that  of  Fig.  179. 

The  anterior  corpora  quadrigemina  are  exactly  halved.  Away  from  the  cut 
surface  of  the  crus  cerebri,  the  pulvinar  and  the  corpora  geniculata  are  seen  in  the 
interior  of  the  section  on  the  right.  The  development  of  the  pes  pedunculi  from  the 
capsula  interna  becomes  especially  clear  upon  comparison  of  this  section  with  those 
made  farther  anteriorly,  because  the  egress  of  the  peduncles  from  the  base  of  the 
brain  is  so  plainly  visible  here. 


292 


ANATOMY    OF    THE    CENTRAL    NERVOUS    SYSTEM. 


The  optic  radiation  has  already  entered  its  terminals  in  the  section  shown  in 
Fig.  185;  we  see  it  only  as  a  gray  area,  in  transverse  section,  in  the  midst  of  the 
white  medullary  substance  lateral  to  the  ventricle. 

The  section  shown  in  Fig.  187  passes  down  just  in  front  of  the  posterior  end 
of  the  corpus  callosum.  This  very  instructive  section  allows  us  to  observe  how  the 
tapetum  of  the  corpus  callosum  develops  from  the  fibers  of  the  splenium,  and  how 
the  tapetum  envelops  the  posterior  horn  of  the  ventricle  and  covers  the  inner  side 
of  the  cornu  Ammonis.  A  part  of  the  hippocampal  gyrus — a  part  that  is  atrophied, 
it  is  true — still  lies  directly  under  the  corpus  callosum  in  man.  It  is  designated  as 
the  fasciola  cinerea.  The  cornu  Ammonis  is  here  met  with  in  its  most  posterior 


Cornu  Ammonis 

Fiss.  parieto-occip. 
Gyrus  lingnalis 

Gvrus  ftisiformis     *»- 


Fig.  188. 


position,  just  in  front  of  the  occipital  lobe.  The  ventricle  opens,  on  the  one  hand, 
posteriorly  into  the  posterior  horn,  and,  on  the  other,  ventrally  into  the  inferior 
horn.  It  is  for  this  reason  that  it  appears  so  long  and  wide.  Outside  of  the  optic 
radiation  lies  the  longitudinal  bundle  which  passes  from  the  occipital  lobe  into  the 
temporal  lobe.  In  the  most  dorsal  territory  the  medulla  still  belongs  to  the  radia- 
tion from  the  uppermost  portion  of  the  two  central  gyri ;  then  follows,  farther 
laterally  and  externally,  the  territory  of  the  parietal  lobe,  and  thereupon  the  medulla 
of  the  gyrus  angularis  and  the  temporal  gyri. 

The   section   illustrated   in   Fig.    188   lies   directly   at   the  base   of  the   cuneate 
occipital  lobe,  consequently  behind  the  end  of  the  corpus  callosum.     The  ventricle, 


BASE    OF   BRAIN,    OPTIC   NERVE,    AND   CORPORA    QUADRIGEMINA.       293 

widely  opened  and  covered  by  the  tapetum,  leads  at  its  dorsal  end  into  the  posterior 
horn;  at  its  ventral  end,  however, — where  mesially  the  gyrus  hippocampi  is  still 
found  to  be  cut, — it  leads  into  the  inferior  horn  of  the  temporal  lobe.  Dorsal  to 
the  cornu  Ammonis  is  found  the  large  mass  of  fibers  of  the  corpus  callosum,  which 
pass  from  the  terminals  in  the  occipital  lobe  to  the  forceps  major  (Balkentoulst)  and 
are  here  cut  just  before  they  enter  the  splenium. 

We  now  meet  with  the  radiatio  occipito-thalamica  in  greater  width  than 
hitherto  outside  of,  and  lateral  to,  the  tapetum.  It  here  lies  under  the  convolu- 
tions of  the  temporal  lobe,  and  this  position  explains  why  lesions  in  the  gyrus 
marginalis  or  angularis  frequently  lead  to  hemianopsia.  If  the  lesions  are  not 
altogether  too  superficial,  they  always  of  necessity  involve  the  optic  radiation. 


Fore.  corp.  callos. 

Cunens 

Rad.  occipito-thalam. 

Fisg.  calcarina 

Ventriculus 

Gyrus  lingualis 

Fasc.  long.  inf. 


Gyrus  fusiform  is 


Fig.  189. 


The  fasciculus  longitudinalis  inferior  also  (the  tract  from  the  occipital  lobe  to 
the  temporal  lobe),  the  transverse  section  of  which,  as  in  the  previous  sections,  you 
again  find  external  to  the  optic  radiation,  is  here  wider  than  previously,  because  we 
now  approach  the  territory  where  it  originates.  The  peculiar  oblique  form  of  the 
under  side  of  the  section  is  explained  from  the  fact  that  the  hemispheres  of  the 
cerebellum,  separated  by  the  tentorium  alone,  here  lie  against  the  cerebrum. 

You  finally  see  a  section  (Fig.  189)  which  1  have  made  through  the  occipital 
lobe  very  near  to  the  posterior  pole  of  the  brain.  The  posterior  horn  of  the  ventricle, 
which  is  still  just  visible  as  a  small  fissure,  may  again  serve  as  a  point  of  orientation 
in  obtaining  the  relation  of  the  fibre-systems  to  one  another  and  as  a  whole. 

From  the  neighborhood  of  the  fissura  calcarina,  which  here  cuts  in  deeply, 
arises  the  optic  radiation,  which  we  have  now  traced  from  its  origin  to  its  termi- 


294  ANATOMY    OF   THE    CENTRAL   NERVOUS    SYSTEM. 

nation  in  the  territory  of  the  thalamus  and  in  the  corpora  quadrigemina.  The  last 
radiations  of  the  occipital  fibers  of  the  corpus  callosum,  the  forceps,  are  separated 
and  distinct  from  the  gray  matter  of  the  ventricle.  The  fasciculus  occipito-tem- 
poralis,  or  longitudinalis  inferior,  lies  now  no  longer  lateral,  but  ventral,  to  the 
ventricle. 

The  greater  part  of  the  remaining  white  matter  visible  in  the  section  belongs  to 
the  intrinsic  fibers  of  the  occipital  lobe,  to  the  short  pathways  which  connect  its 
various  cortical  areas  with  one  another. 

It  is  not  improbable  that  the  fibers  found  in  the  optic  radiation  have 
two  points  of  origin:  they  may  originate  from  the  cells  of  the  primary 
centers  and  pass  to  the  cortex,  or  they  may  originate  from  cortical  cells  and 
pass  to  these  primary  centers. 

In  cases  of  destructive  focal  lesion  in  the  occipital  lobe  and  in  the  most 
posterior  part  of  the  internal  capsule,  disturbances  of  sight  appear  that  are 
exactly  similar  to  those  where  the  optic-nerve  tract  has  been  injured  on  the 
side  involved.  The  outer  half  of  the  retina  of  the  eye  which  is  on  the  same 
side  as  the  lesion  and  the  inner  half  of  the  retina  of  the  opposite  eye 
degenerate. 

A  fiber-tract  that  was  discovered  by  Gall  and  Spurzheim  probably  belongs  to 
the  system  of  the  opticus  also.  It  passes  down  laterally  from  the  anterior  corpora 
quadrigemina,  and  at  the  base  of  the  brain  runs  for  a  distance  transversely  across 
the  pes  pedunculi  before  it  sinks  into  the  pes  near  to  the  median  line.  It  then 
attains  a  ganglion  of  the  ventral  thalamic  region  (Kolliker).  This  tract — the 
tractus  peduncularis  transversus — degenerates  after  the  destruction  of  one  optic 
tract  (Gudden).  It  is  not  always  capable  of  demonstration,  and  is  variable  in  its 
development.  In  Fig.  141  you  see  it  (not  designated)  pass  over  the  right  crus 
cerebri.  Probably  this  bundle  is  identical  with  that  one  which  was  described  on 
page  132  as  the  tractus  thalamo-tectalis. 


CHAPTER    XIX. 

• 

THE  TEQMENTUM  AND  THE  PEDUNCLE  OF  THE  MIDBRAIN. 

THE  frontal  sections  through  the  cerebrum,  with  description  of  which 
the  previous  chapter  ended,  led  us  somewhat  away  from  the  tracing  of  the 
tracts  which  pass  into  and  beyond  the  midbrain. 

In  the  description  these  tracts  had  been  followed  to  the  region  of  the 
posterior  end  of  the  middle  or  third  ventricle.  One  may  see  in  Fig.  125 
that  just  behind  this  the  midbrain — the  corpora  quadrigemina — begins.  At 
that  place  the  thalami  diverge  from  each  other,  the  tegmental  prominence 
pushes  in  between  them,  thus  considerably  decreasing  the  depth  of  the 
ventricle. 

In  connection  with  the  accompanying  description,  study,  in  Fig.  190, 
the  formation  of  the  roof  of  the  midbrain.  In  the  most  anterior  part  of 
this  roof  (see  also  Fig.  125)  lie  the  fibers  of  the  posterior  commissure,  close 
behind  which  lie  the  corpora  quadrigemina.  The  narrow  ventricle  which 
passes  under  the  roof  has  received,  in  the  region  of  the  midbrain,  the  name 
aquceductus  Sylvii.  The  entrance  to  the  aqueduct  lies  just  under  the  pos- 
terior commissure.  The  aqueduct  is  everywhere  surrounded  by  the  gray 
matter  of  the  central  canal. 

Now  the  posterior  commissure  lies  in  the  most  anterior  portion  just 
behind  the  epiphysis.  A  part  of  its  fibers  arises  from  ganglia  which  lie, 
one  on  each  side,  near  the  median  line,  deeply  imbedded  in  the  interbrain. 
This  is  easier  to  demonstrate  in  lower  vertebrates  than  in  mammals,  but 
Kolliker  has  also  shown  that  in  mammals  the  origin  is  the  same.  Thence 
they  pass  upward  to  the  surface  and,  anterior  to  the  quadrigeminal  bodies, 
turn  to  the  opposite  side.  They  pass  for  only  a  very  short  distance  hori- 
zontally, when  they  plunge  into  the  depth  of  the  tegmentum  of  the  mid- 
brain,  through  which  they  pass  farther  back. 

As  very  clearly  seen  in  lower  vertebrates,  the  majority  of  the  fibers  in 
question  pass  laterally  and  ventrally  from  the  posterior  longitudinal  fascicle 
into  the  medulla.  Through  this  reinforcement  this  fascicle  becomes  a 
thick  bundle — later  to  be  described.  Spitzka  and  Darkschewitsch  have 
seen  a  similar  arrangement  in  mammals.  In  all  vertebrates  the  posterior 
commissure  is  one  of  the  first  bundles  to  become  medullated. 

We  come  now  to  the  region  of  the  midbrain.  Let  us  find  what  has 
become  of  all  the  fibers  which  were  traced  in  the  last  chapter.  "We  find 
only  a  few  in  the  region  which  we  have  now  reached.  The  greater  part  of 

(295) 


296  ANATOMY    OF   THE    CENTRAL    NERVOUS    SYSTEM. 

the  fibers  which  compose  the  medullary  substance  of  the  brain-mantle  is  not 
to  be  seen  in  the  posterior  sections  of  the  interbrain.  They  have  either,  as 
association-tracts,  disappeared  in  the  cortex  itself  or  as  coronal  fibers  of 
the  thalamus  disappeared  in  the  ganglia  of  the  thalamus.  A  portion  of  the 
corona  radiata,  passing  beneath  the  interbrain,  arrives  at  the  base  of  the 
brain  as  the  pes  pedunculi  cerebri.  Even  the  fiber-system  of  the  striatum  has 
almost  completely  disappeared,  only  a  bundle  to  the  substantia  nigra  Som- 
meringi  being  still  demonstrable  (see  Fig.  191). 


•:•:  ••^-WJiii       // 

/  ',        ^mri'\U        II    H*ub#£tvhta*3 

***••   i  m,  a  / '        &*& 
^'^JLL  ^^^ 

7hakm;ji  Zur  Zrus^. — 


Central' 

,   Kanal 


Fig.  190. — Median  sagittal  section  through  the  interbrain  and  the  structures 
posterior  to  it.  The  course  of  a  number  of  coronal  fibers  is  indicated  by  lines: 
Zur  Briicke,  To  the  pons.  Pyramiden  Fasern,  Pyramidal  fibers.  Haubenstrahlung, 
Tegmental  radiation.  Zu  den  Opticuscentren,  To  the  opticus  centers.  Haute, 
Tegmentum.  Pyramidenkreuzung,  Pyramidal  decussation. 

In  the  plane  of  the  last  section  a  part  of  the  lamince  medullares  thalami 
and  especially  a  lateral  bundle,  the  superior  lemniscus  from  the  thalamus, 
may  be  traced.  Furthermore  a  few  small  bundles  which  arise  from  the 
corpus  mamillare  and  the  Ggl.  habenulae  may  be  seen. 

Having  now  made  ourselves  somewhat  familiar  with  the  structures  in 


THE    TEGMEXTIIM    AXD    THE    PEDUNCLE    OF    THE   MIDBRAIX. 


297 


the  region  of  the  corpora  quadrigemina,  let  us  study  a  section  through  the 
anterior  quadrigeminal  bodies,  the  structures  of  the  tegmentum,  and  the 
pedunculi  cerebri  (see  Fig.  192). 

Taking  bearings  from  structures  already  known,  note  on  each  side  ex- 
ternally the  pulvinar  thalami,  from  which  the  optic  nerve  appears  to  come. 
The  corpus  geniculatum  laterale  seems  to  be  inclosed  in  the  course  of  the 


Fig.  191.- — Showing  the  transition  from  the  interbrain  to  the  midbrain.  The 
section  is  from  the  brain  of  a  dog  and  is  about  one  millimeter  posterior  to  that 
shown  in  Fig.  177.  Compare  carefully  the  series  represented  in  Figs.  169,  176, 
177,  and  191.  NOTE:  the  Commissura  post.,  whose  most  anterior  fibers  are 
severed;  the  stratum  sonale,  fibers  from  the  anterior  quadrigeminal  bodies  into 
the  opticus;  the  pulvinar;  the  Nuc.  ventralis  thalami;  the  Superior  lemniscus 
or  fillet  (Obere  Schleife),  which  is  nearer  the  median  line  and  larger  than  in 
Fig.  177;  the  fasciculus  retroflexus,  which  has  passed  off  from  the  ggl.  haben- 
ulae;  the  most  anterior  fibers  of  the  inferior  lemniscus  (Unt.  Schleife),  which 
arises  from  a  gray  nucleus  that  merges  into  the  median  marrow  of  the  corpora 
quadrigemina;  the  most  anterior  fibers  of  the  oculo-motorius  (Radices  N.  Ill); 
the  posterior  longitudinal  fascicle,  which  arose  in  the  preceding  section  by  a 
few  fibers  from  its  nucleus,  now  grown  larger;  the  optic  radiation  (Sehstrahl- 
una),  which  is  the  pedicle  of  the  anterior  quadrigeminal  body  and  of  the  cor- 
pus geniculatum  laterale.  The  large  nucleus,  designated  Nucl.  ventr.  thalami 
gradually  merges  below  into  the  corpus  geniculatum  mediale.  Note  also  the 
decussation  between  the  cornua  Ammonis  and  the  position  of  the  fornix  longus. 
In  the  pes  pedunculi  the  stratum  intermedium  composed  of  fibers  from  the 
lenticular  ganglion  in  the  regio  subthalamica. 


298 


ANATOMY    OF    THE    CEXTBAL    NEBVOUS    SYSTEM. 


nerve  (see  especially  Fig.  195).  It  receives  a  bundle  from  the  arm  of  the 
corpus  qiiadrigeminum  anterius.,  well  shown  on  the  left  side  of  the  figure, 
above  which  one  will  recognize  the  corpus  geniculatum  mediak.  Beneath 
the  pulvinar  the  pes  pedunculi  emerges. 

In  the  pes  are  contained  fibers  of  very  varied  origin.  Embryological 
studies  and  especially  the  exact  tracing  of  secondary  degenerations,  which 
result  from  cerebral  lesions,  alone  make  it  possible  to  determine  where  the 
different  tracts  lie.  There  is  already  a  considerable  number  of  well  observed 
cases  of  partial  degeneration  of  the  pes,  so  that  an  enumeration  of  the  parts 
of  the  pes  may  with  due  certainty  be  given.  According  to  Dejerine's  in- 


Cnrpus  genlc. 


Si/fistanfia  ninra . 
Ifintcrts  Lancjsbuiiflel . 


Fig.  192.— Cross-section  through  the  corpora  quadrigemina  anteriora  (some- 
what diagrammatic).  Vordere  Yierhiigel,  Corp.  quad.  ant.  Arm  des  Vierli.,  Arm 
of  the  corp.  quad.  Htnibe,  Tegnientum.  Fuss,  Crusta,  or  pes  pedunculi  cerebri. 
Schleife,  Lemniscus,  or  fillet.  Hinteres  Lanysbiindel,  Fasciculus  longitudinalis 
post.  Rother  Kern,  Nucleus  ruber. 


vestigations,  which  cover  the  largest  amount  of  material  yet  studied,  there 
lie  in  the  outer  fifth  of*  the  pes  fibers  which  arise  from  the  middle  part  of 
the  temporal  lobe.  In  its  median  fifth  are  fibers  which  pass  down  from  the 
region  of  the  operculum.  In  the  middle  three-fifths  of  the  pes  are  found 
the  fibers  from  the  posterior  portion  of  the  frontal  lobe  and  from  the  true 
motor  region.  All  of  these  bundles  arise  direct  from  the  cortical  cells  and 
degenerate  when  they  are  interrupted  anywhere  between  the  cortex  and 


THE    TEGMENTUM    AXD    THE    PEDUNCLE    OF    THE    MIDBEAIN.  299 

the  pons.  In  about  the  middle  third  of  the  pes,  beneath  these  bundles,  lies 
also  the  tractus  cortico-spinalis,  the  pyramidal  tract,  the  only  bundle  of  the 
pes  which  extends  farther  than  the  pons. 

Dorsal  from  the  pes  pedunculi  lies  the  stratum  intermedium  (see  Fig. 
191),  with  fibers  from  the  corpus  striatum;  then  comes  the  substantia 
nigra,  an  aggregation  of  fine  nerve-fibrils  and  ganglion-cells,  the  significance 
of  which  is  still  quite  unknown. 

In  the  tegmentum  one  notices  at  once  the  two  large,  round,,  reddish- 
gray  bodies;  they  are  the  red  nuclei  of  the  tegmentum:  nuclei  rubri  teg- 
menti,  or  nuclei  legmenti.  The  corpus  subthalamicum  which  lies  near  them 
(see  Fig.  179)  does  not  appear  in  the  plane  of  this  section. 

The  red  nucleus,  into  which  fibers  pass  from  the  thalamus  and  from 
the  cerebral  cortex,  is  at  this  point  rich  in  medullated  fibers.  These  pass 
ventral  to  the  posterior  quadrigeminal  bodies,  and,  for  the  most  part,  decus- 
sate there  with  those  of  the  opposite  side.  They  belong  to  the  anterior 
cerebellar  peduncle  and  the  decussation  is  called  the  decussation  of  the 
anterior  (superior)  cerebellar  peduncles.  This  decussation  is  very  promi- 
nent in  a  frontal  section  through  this  region.  Farther  posterior  these  tracts 
— Tractus  tegmento-cerebellares — form  thick  bundles  which  lie  external 
to  the  red  nuclei,  and  then  pass  farther  and  farther  to  the  side  and  finally 
reach  the  outer  surface,  whence  they  pass  backward  to  the  cerebellum. 
Since,  after  injury  of  the  cerebellum,  the  superior  peduncle  degenerates  as 
far  as  the  tegmental  nucleus,  its  origin  must  be  in  the  cerebellum  and  its 
end  in  the  red  nucleus  (Mahaim,  et  al.}. 

A  nearly  horizontal  section  through  the  thalamus,  the  corpora  quadri- 
gemina,  and  the  cerebellum,  following  the  plane  of  the  superior  peduncles, 
gives  the  relations  between  the  thalamus,  the  red  nucleus,  the  tegmental 
radiation,  superior  peduncles,  and  cerebellum,  as  shown  in  Fig.  193. 

In  the  cerebellum  the  superior  peduncle  enters  the  corpus  dentatum. 

Exterior  to  the  tegmental  nucleus  lies  a  thick  bundle  of  obliquely-cut 
fibers  (see  Fig.  192),  which  appear  to  emerge  from  under  the  corpora  quadri- 
gemina.  They  pass  downward  in  the  region  dorsal  to  the  substantia  nigra. 
The  fibers  arise  mostly  from  the  ganglia  of  the  corpora  quadrigemina  and 
are  called  the  inferior  lemniscus,  or  lower  fillet.  The  upper  fillet  from  the 
thalamus  lies,  at  the  level  now  being  considered  (see  Figs.  191  et  seq.), 
somewhat  external  to  and  below  the  red  nucleus,  and  appears  as  a  separate 
bundle  of  transversely  divided  fibers.  To  the  outside  of  it  lie  the  fibers  of 
the  lower  fillet.  It  thus  happens  that  there  is  a  broad  band  of  transversely 
divided  fibers  just  above  the  substantia  nigra,  which  is  called  the  layer  of 
the  fillet,  or  stratum  lemnisci  (see  also  Fig.  194). 

The  greater  part  of  the  stratum  lemnisci  can  be  traced  posteriorly  as  far  as  the 
nuclei  of  the  sensory  nerves  and  of  the  posterior  columns.  Meynert  first  demon- 


300 


ANATOMY    OF    THE    CENTRAL    NERVOUS    SYSTEM. 


strated  that  in  it  we  have  a  segment  of  the  sensory  tract.  Embryology  and  com- 
parative anatomy  equally  substantiate  this  position.  Later  we  shall  trace  the  farther 
course  of  the  fillet. 

Thus  the  stratum  lemnisci  contains  two  elements:  mesially  the  upper 
and  laterally  the  lower  lemniscus.  The  lower  lemniscus  (better  called  lem- 
niscus  of  the  midbrain)  arises  chiefly  from  a  system  of  fibers  not  yet  men- 
tioned: viz,  the  deep  marrow,  or  deep  medullary  stratum  of  the  midbrain- 
roof ;  the  remainder  arises  from  the  ganglion  of  the  corpus  quadrigeminum 


Trw:/-. 
eyrf/c 


Fig.  193. — Diagrammatic  horizontal  section  through  the  decussation  of  the 
superior  cerebellar  peduncles  and  vicinity.  The  bundle  to  the  optic  tract  is 
questionable.  Direkte  Fasern  sum  Thalamus,  Direct  fibers  to  the  thalamus. 
Haubenstrahlimg,  Tegmental  radiation.  Rother  Kern,  Tegmental  nucleus.  Re- 
gion der  YirMffel,  Region  of  the  corpora  quadrigemina.  Bindearm,  Anterior  or 
superior  cerebellar  peduncle. 


postering.     On  an  oblique  frontal  section  through  both  pairs  of  quadri- 
geminal  bodies  this  is  clearly  shown  (see  Fig.  194). 

The  ganglion  in  question  consists  of  a  large,  round  nucleus  filled  with 
a  net-work  of  fine  fibers.     As  the  ganglion  of  the  posterior  quadrigeminal 


THE    TEGMENTUil    AND    THE    PEDUNCLE    OF   THE    MIDBRAIN. 


301 


body  possesses  only  one  nucleus,  it  does  not  show  the  stratification  of  gray 
and  white  substance  characteristic  of  the  anterior  quadrigeminal  body — the 
optic  ganglion.  It  is  connected  with  the  ganglion  of  the  opposite  side 
through  fibers  which  pass  over  the  aqueduct  of  Sylvius. 

Phylogenetically  the  deep  medullary  stratum  is  a  very  old  system.  It 
is  not  lacking  even  in  the  most  simply  constructed  brains  of  the  lower  verte- 
brates, and  in  these,  as  in  the  human  brain,  its  fibers  become  medullated 
very  early.  Its  fibers  arise  in  the  roof  of  the  midbrain  from  layers  which  lie 
ventral  to  those  from  which  the  optic  nerve  arises.  From  this  origin  they 
pass  radially  inward,  but  turn  ventrally  near  the  central  gray  matter  which 
surrounds  the  aqueduct.  The  most  lateral  of  these  fibers,  united  with  those 


Fig.  194. — An  oblique  frontal  section  in  the  plane  indicated  in  the  acces- 
sory figure  (Schnittrichtung)  contains  the  greater  part  of  the  origin  of  the  lower 
lemniscus  (or  midbrain- fillet).  Hsematoxylin  stain.  For  Brack,  ant.  read 
brachium  posticum.  Tiefes  Mark,  Deep  medullary  stratum.  Centr.  Hohlengrau, 
central  gray  matter.  Schleifenschicht  d.  Pons,  Stratum  lemnisci  pontis.  Schnitt- 
richtung, Direction  of  section. 


which  come  from  the  opposite  side,  pass  into  the  fillet,  but  the  more  mesial 
ones  engirdle  the  aqueduct  and  mostly  decussate  ventral  to  it  with  those 
of  the  opposite  side:  "fountain-like"  decussation  (Forel).  (See  Figs.  195 
and  199.) 

In  fishes  and  birds  the  fibers  of  the  deep  medullary  layer  are  so  strongly 
developed  that  their  course  is  easier  to  recognize.    But  in  them  as  in  the 


302 


ANATOMY    OF    THE    CENTRAL    NERVOUS    SYSTEM. 


amphibians  and  reptiles,  one  recognizes  that  these  fibers,  so  far  as  they  do 
not  pass  into  the  fillet,  belong  to  the  midbrain  itself  and  end  in  cells  partly 
on  the  same  side  and  partly  on  the  opposite  side.  At  the  corresponding 
point  in  the  human  brain  there  are  also  groups  of  cells,  the  ganglion  pro- 
fundum  mesencephali  laterale  et  mediale. 

Scattered  cells  in  the  base  of  the  midbrain  probably  give  origin  to  a  system  of 
fibers,  very  interesting  phylogenetically.  It  will  be  recalled  that  in  bony  fishes  at 
this  location  there  is  a  large  ganglion,  the  Torus  semicircularis,  and  that  from  it  a 
large  bundle  may  be  followed  into  the  lateral  tracts.  Boyce  has  recently  succeeded 
in  finding,  in  a  cut  through  one  side  of  the  brain  of  a  cat,  a  bundle  which,  begin- 
ning in  the  base  of  the  midbrain,  may,  through  operatively  induced  degenerations, 


Fig.  195. — Fibers  arising  in  the  roof  of  the  midbrain.     Dorsally  the  Tractus 
opticus,  ventrally  the  deep  medullary  layer  (Tiefes  Mark).     Diagrammatic. 


be  followed  out  of  the  midbrain  as  far  downward  as  the  anterior  and  lateral  col- 
umns of  the  spinal  cord. 

In  the  central  gray  matter,  below  the  quadrigeminal  bodies,  appear  the 
first  ganglion-cells  which  give  rise  to  a  cranial  nerve:  nervus  oculo-motorius. 
From  their  union,  the  nucleus  nervi  oculo-motorii,  the  root-fibers  of  the 
nerve  pass  ventrally  through  the  tegmentum  and  the  crusta  toward  the  base 
of  the  brain,  where  they  pass  out  united  into  thick  bundles  (see  Fig.  199). 
The  motor-oculi  nerve  contains  fibers  to  several  muscles  within  and  about 
the  eye.  Since  nuclear  paralysis  of  individual  muscles  of  the  group  supplied 
by  this  nerve  has  been  observed,  it  is  very  probable  that  the  nucleus  con- 
sists of  a  complex  of  small  nuclei,  somewhat  separated  from  one  another. 


THE    TEGMENTUM   AND    THE    PEDUNCLE    OF   THE    MIDBRAIN. 


303 


In  man  a  manifest  division  into  several  portions  may,  in  fact,  be  observed. 
Quite  forward,  partly  in  the  wall  of  the  third  ventricle,  lies,  on  either  side, 
a  narrow,  small-celled  nucleus,  the  nucleus  anterior.  It  sends  its  few  fibers 
somewhat  backward  to  the  main  trunk  of  the  nerve.  Posterior  to  it  lies  the 
nucleus  posterior,  composed  of  large,  multipolar  cells  and  extending  along 
nearly  the  whole  length  of  the  aqueduct.  One  may  recognize  in  this  nucleus 
an  arrangement  of  the  cells  into  groups.  One  dorsally  located  collection 
of. cells  is  clearly  distinguishable.  While  all  the  other  motor-oculi  fibers 


Fig.  196. — Floor  of  the  aquseductus  Sylvii,  looking  upward.     Nuclei  of  the 
motor-oculi  and  trochlearis  nerves.     Partly  diagrammatic. 


emerge  from  the  side  in  which  they  originate,  the  fibers  from  this  group,  as 
discovered  by  Gudden,  pass  toward  the  median  line,  dip  ventrally,  and  cross 
to  the  opposite  side.  Besides  the  dorsal  division,  a  median  one  may  be  de- 
fined. It  lies  exactly  in  the  median  line  and  sends  out  root-fibers  both  to 
the  right  and  left. 

Fig.  196  represents  partly  diagrammatically  the  nuclei  in  the  floor  of 
the  aqueduct  and  their  relations  to  the  nerve-roots.  Note  in  the  figure  two 
small  nuclei  joined  together  anteriorly  (a  and  &).  These  two  nuclei,  first 


304  ANATOMY    OF   THE    CENTRAL   NERVOUS    SYSTEM. 

seen  by  me  in  fetal  brains  and  since  more  carefully  studied  by  "Westphal  in 
adult  brains,  lie  in  a  dense  net-work  of  nerve-fibers.  It  is  not  yet  certain 
whether  these  fibers  are  in  connection  with  the  motor-oculi  nerve,  and  if  so 
how  the  connection  is  made.  There  is  such  an  array  of  clinical  observations 
and  of  facts  derived  from  post-mortem  dissections  that  one  may  venture  to 
designate  the  portion  of  the  nucleus  from  which  the  innervation  of  each 
individual  ocular  muscle  comes.  I  give  here  Starr's  table,  the  latest  of  these 
numerous  attempts  so  happily  begun  by  Pick.  According  to  Starr,  the 
nuclei  of  the  individual  muscles  are  arranged  from  before  backward  thus: — 

Sphincter  iridis.  Musculus  ciliaris. 

Levator  palpebrae.  Rectus  internus. 

Rectus  superior.  Rectus  inferior. 
Obliquus  inferior. 

The  nerves  for  the  intrinsic  muscles  of  the  eye  arise  probably  from  the 
anterior  nucleus.  The  crossed  tract,  possibly  also  the  median  portion  of  the 
posterior  nucleus,  are  to  be  accredited  to  the  internal  rectus.  Clinical  ob- 
servations show  that  there  must  be  a  direct  and  a  crossed  connection  be- 
tween the  motor-oculi  nerve  and  the  centers  of  the  optic  nerve,  but  the 
anatomical  basis  for  this  has  not  yet  been  established.  Net-works  and 
bundles  of  fibers  through  which  the  connection  might  take  place  are  abun- 
dant in  this  region.  But  up  to  the  present  time  there  has  been  on  this  point 
neither  a  conclusive  experiment  nor  a  convincing  clinical  observation  with 
a  subsequent  post-mortem  demonstration. 

The  motor-oculi  nucleus  lies  ventral  to  the  aqueduct  of  Sylvius: 
i.e.,  in  the  floor  of  the  aqueduct.  Later,  as  we  proceed  to  study  the  teg- 
mentum  backward,  we  will  meet  in  the  region  of  this  floor  the  nuclei  of 
nearly  all  the  other  cranial  nerves. 

At  the  beginning  of  this  chapter  it  was  stated  that  fibers  pass  backward 
from  the  posterior  commissure.  Toward  a  point  located  mesially  and  ven- 
trally  from  these  fibers  fine  bundles  converge,  which  arise  in  the  interbraiu 
below  the  anterior  nucleus  of  the  oculo-motorius.  The  sectional  area  covered 
by  these  bundles  becomes  progressively  greater  from  before  backward.  They 
are  reinforced  by  many  fibers  from  the  motor-oculi  nucleus  itself.  We  shall 
meet  the  somewhat  triangular  cross-section  of  this  fascicle,  which  is  made 
up  of  such  varied  constituents,  in  all  the  sections  from  the  corpora  quadri- 
gemina  down  to  the  beginning  of  the  spinal  cOrd.  It  is  called  the  posterior 
longitudinal  fascicle  (fasciculus  longitudinalis  posterior).  Since  along  the 
whole  course  of  this  bundle  fibers  pass  from  it  to  the  nuclei  of  the  other 
cranial  nerves  (readily  seen  in  a  fetus  of  six  or  seven  months,  where  few 
other  fibers  are  medullated),  and  since  its  posterior  end  lies  much  beyond  the 
nucleus  of  the  abducens  it  is  probable  that  the  posterior  longitudinal  fascicle 


THE    TEGMENTUil   AND    THE    PEDUNCLE    OF    THE    MIDBKAIN. 


305 


contains,  besides  the  fibers  which  connect  the  ocular  muscles  among  them- 
selves, also  fibers  for  the  other  cranial  nerves. 

The  posterior  longitudinal  fascicle  sends  its  most  anterior  fibers  much 
farther  forward  than  to  the  nucleus  of  the  oculo-motorius.  In  the  central 
gray  matter  just  anterior  to  the  beginning  of  the  aqueduct  is  a  collection  of 
large  ganglion-cells  from  which  a  number  of  such  fibers  arise, — nucleus 
fasciculi  longitudinalis  superioris  (see  Fig.  179).  This  nucleus  is  demon- 
strable in  all  vertebrates.  In  mammals  it  lies  in  those  planes  which  ven- 
trally  intersect  the  posterior  part  of  the  corpus  mamillare.  Inasmuch  as  it 
is  found  in  all  vertebrates,  and  always  from  the  interbrain  to  the  region 
of  the  anterior  columns  of  the  spinal  cord,  it  must  be  recognized  as  one  of 


Fig.  197. — Longitudinal,  nearly  median,  section  through  the  midbrain  of  a 
twenty-eight  weeks'  human  fetus,  partly  through  the  outer  wall  of  the  aque- 
duct, showing  the  end  of  that  part  of  the  posterior  longitudinal  fascicle  which 
belongs  to  the  nucleus  of  the  oculo-motorius.  Vierhugelplatte,  Midbrain-plate. 
Hint.  LangsMndel,  Post.  long,  fascicle.  Hirnschenkel,  Pes  pedunculi. 


the  fundamental  features  of  the  brain.     (See  also  Chapter  VI,  Figs.  43 
and  44,  and  text). 

The  boundaries  of  the  numerous  systems  of  fibers  to  be  found  in  the 
region  of  the  corpora  quadrigemina  can  only  be  sharply  differentiated 
through  studying  the  development  of  their  medullary  sheaths.  In  Fig.  198 
we  have  a  section  from  a  nine  months'  human  fetus,  through  the  anterior 
quadrigeminal  bodies  just  at  the  posterior  commissure.  All  of  the  fibers, 
which  at  this  stage  of  development  are  medullated,  are  stained  with 
hffimatoxylin. 


306 


ANATOMY    OF    THE    CENTRAL    NERVOUS    SYSTEM. 


Of  the  structures  named  in  the  figure  the  small  elliptical  areas  (&),  lying 
between  the  red  nuclei,  have  not  been  previously  mentioned.  The  fibers 
here  cut  arise  in  the  ganglion  habenulae  thalami  and  pass  from  it  downward 
and  backward  to  a  small  ganglion,  which  lies  between  the  cerebral  peduncles, 
the  ganglion  interpedunculare.  Before  entering  this  ganglion  the  fibers 
decussate.  The  bundle  is  called  the  tractus  habenulo-peduncularis,  the  Fas- 
ciculus retroflexus,  or  Meynert's  bundle.  Its  course  is  best  seen  in  Fig.  144. 
In  the  ganglion  habenulas  ends  the  greater  part  of  the  taenia  thalami,  which, 
as  above  described,  passes  up  from  the  lateral  portions  of  the  olfactory  area. 

The  ganglion  interpedunculare  was  discovered  by  Gudden  and  first  exactly 
described  by  Forel.  Gudden  showed  that  after  destruction  of  one  ganglion  haben- 
ulse  the  fasciculus  retroflexus  of  the  same  side  undergoes  descending  degeneration, 


ci  opt, 


Fig.  198. — Frontal  section  through  the  anterior  quadrigeminal  bodies  of  a 
nine  months'  fetus,  o.  8.,  u.  8.,  upper  fillet  and  lower  fillet.  Hint.  Langsb., 
posterior  longitudinal  fascicle. 


and  that  the  degenerated  fibers  may  be  followed  as  far  as  the  opposite  ganglion 
interpedunculare.  Canser  discovered  another  bundle  from  the  tegmentum  to  the 
ganglion  interpedunculare. 

The  author's  investigations  on  normal  dogs  and  on  one  in  which  the  habenular 
ganglion  had  been  destroyed  show  still  further  facts:  The  ganglion  interpedunculare 
in  dogs  consists  of  five  different  ganglia,  in  front  two  pear-shaped  bodies  lying  side 
by  side,  covered  by  a  flat  plate  which  lies  besirfe  the  tegmentum;  posteriorly  this 
group  is  inclosed  by  a  much  larger,  horseshoe-shaped  ganglion,  whose  posterior 
portion  constitutes  the  main  body  of  the  ganglion.  The  slender  anterior  limbs  of 
this  ganglion  receive  the  fibers  of  the  Fasciculus  retroflexus,  which  lose  their  med- 
ullary sheaths  immediately  after  their  entrance.  In  the  lizard  the  Golgi  method 
shows  that  after  decussation  they  break  up  into  innumerable  very  fine  terminal 


THE    TEGMEXTU1I    AXD    THE    PEDUNCLE    OF   THE    MIDBRAIN. 


307 


fibrillse.  The  third  ganglion  mentioned  (Deckganglion)  is  filled  with  a  net-work  of 
fine  fibers.  From  this  ganglion  bundles  pass  ventrally  between  the  two  frontal 
ganglia.  An  afferent  bundle  from  the  tegmentum  of  the  midbrain  ends  in  the  two 
pear-shaped  ganglia.  This  bundle  is  of  large  fibers,  which  remain  intact  after  de- 
struction of  the  cerebrum  and  the  thalamus. 

Fig.  199  is  a  composite  from  several  periods  of  development.  In  it 
are  shown  nearly  all  of  the  structures  to  be  found  in  a  section  just  posterior 
to  the  anterior  quadrigeminal  bodies. 


Fig.  199. — Section  just  behind  the  anterior  quadrigeminal  bodies.  A  com- 
posite from  sections  representing  different  stages  of  development  of  medullary 
sheaths.  Hsematoxylin-copper-acetate  method.  (For  Brach.  C.  quad.  ant.  read 
post.)  Ticfes  Mark,  Deep  medullary  stratum.  Centr.  Hohlengrau,  Central  gray 
matter.  Aus  Thalamus,  From  the  thalamus. 


One  may  use  this  figure  to  review  this  chapter,  finding  the  following 
structures: — 


308  ANATOMY   OF   THE    CENTRAL   NERVOUS    SYSTEM. 

1.  Midbrain-roof :  (a)  Corpus  quadrigeminum  anterius,  from  which 
the  optic  nerve  arises  dorsally  and  the  deep  medullary  stratum  ventrally; 
(b)  the  decussation  of  the  latter  above  the  aqueduct;  (c)  the  central  gray 
matter  which  surrounds  the  aqueduct;  (d)  at  the  outer  margin  of  the  central 
gray  matter  lies  a  small  nucleus  (not  before  mentioned),  whose  vesicular  cells 
may  be  found  at  the  same  relative  position  in  all  sections  of  the  midbrain. 
From  it  arises  a  slender  bundle  of  fibers,  which  passes  down,  receiving  acces- 
sions continuously  to  the  pons,  where  it  joins  the  emerging  fibers  of  the 
trigeminus.  It  is  the  midbrain-roof  of  the  nervus  trigeminus.  (Rad.  desc. 
V,  Fig.  199.) 

In  the  roof  of  the  midbrain  one  may  distinguish  a  rather  faint  stratification  of 
alternating  gray  and  white  matter.  The  minute  structure  of  the  layers  is  not 
sufficiently  known  in  the  human  brain.  In  mammals  one  may  generally  differ- 
entiate in  the  anterior  quadrigeminal  body  the  following  layers  from  without  in- 
ward: 1.  Superficial  marrow  and  gray  matter, — the  entering  fibers  of  the  optic 
tract, — atrophies  after  extirpation  of  the  eye,  and  is  rudimentary  in  the  mole 
(Ganser).  2.  Middle  gray  matter,  a  direct  continuation  of  the  superficial  gray 
matter;  best  studied  in  birds,  and,  according  to  Cajal  and  Gehucliten,  it  contains 
numerous  cells  whose  neuraxons  usually  pass  down  into  the  fillet,  but  whose  den- 
drites  break  up  into  twigs  among  the  fine  terminal  ramifications  which  the  optic 
nerve  sends  into  the  superficial  gray  matter.  3.  Middle  marrow.  It  lies  within  and 
below  the  middle  gray  and  contains  bundles  from  the  options  radiation,  but  also 
other  fibers,  as  it  degenerates  only  in  part  after  removal  of  the  corresponding  cor- 
tex. 4.  The  deep  gray  .matter  and  the  deep  marrow,  or  deep  medullary  stratum. 
The  gray  matter  is  the  continuation  of  the  general  gray  matter  of  the  quadrigeminal 
bodies.  The  deep  marrow  contains  the  deep  fibers  of  the  stratum  lemnisci,  which 
spring  from  the  deep  and  middle  gray  of  the  quadrigeminal  body. 

2.  The  Tegmentum :  (a)  In  the  ventral  portion  of  the  central  gray  mat- 
ter, the  nucleus  posterior  medialis  et  lateralis  of  the  nervus  oculo-motorius,  in 
which  pass  fibers  apparently  from  the  deep  marrow  and  some  from  the  pos- 
terior longitudinal  fascicle.    (b)  Lateral  from  and  bordering  on  the  posterior 
longitudinal  fascicle,  the  fibers  of  the  posterior  commissure,     (c)  External 
to  (b)  a  medullated  area  which  comes  from  the  thalamus  and  which  left  it  as 
lamina  medullares;  it  probably  contains  a  bundle  from  the  nucleus  of  the 
trigeminus  to  the  thalamus.     (d}  The  lower  fillet  from  the  quadrigeminal 
bodies,  and  the  upper  fillet  from  the  thalamus.     (e)  The  nucleus  ruber  teg- 
menti,    from   which    arise    numerous   fibers    for    the    superior    cerebellar 
peduncles,     (f)  The  "fountain-like"  tegmental  decussation.     (g)  The  fas- 
ciculus retroflexus. 

3.  On  the  boundary  between  the  crusta  and  the  tegmentum  one  recog- 
nizes the  substantia  nigra  Sommeringi,  into  which  numerous  fibers  (the 
stratum  intermedium]  pass  from  the  nucleus  lentiformis. 

4.  The  Pes  Pedunculi:    (a)  The  pyramidal  tract  is  shown  still  non- 
medullated,  as  it  appeared  in  a  specimen  from  a  child  four  weeks  of  age. 


THE    TEGMENTUM    AND    THE    PEDUNCLE    OF   THE    MIDBRA1X.  309 

(&)  The  fibers  which  lie  on  the  median  side  of  the  pyramis  originate  in  the 
bbns  frontalis,  those  which  lie  outside  of  it,  in  the  lobus  parietalis  et  tem- 
poralis.  (c)  A  bundle  leaves  the  pyramid  at  this  point  and,  skirting  the 
border  of  the  pes,  joins  the  fillet  farther  back,  forming  the  median  layer 
of  that  structure.  Spitzka  makes  it  probable,  on  comparative  anatomical 
grounds,  that  this  bundle  contains  the  cerebral  tracts  of  the  cranial  nerves. 
(d)  Internal  to  it  are  visible  the  root-fibers  of  the  motor-oculi  nerve,  (e)  Just 
before  their  emergence  they  traverse  the  pedunculus  corporis  mamillaris. 

The  course  of  the  fibers  in  the  thalamic  and  subthalamic  region  is  less  thor- 
oughly known  than  in  most  other  regions  of  the  brain.  In  this  obscure  field,  Meynert, 
Forel,  Gudden,  Flechsig,  Ganser,  Wernicke,  Monakow,  Kolliker,  the  author,  and 
others  have  worked. 

The  origin  of  the  optic  nerve  has  been  investigated  by  Meynert,  J.  Stilling, 
Tartuferi,  Gudden,  Bellonci,  and  by  Monakow  (to  whom  we  are  indebted  for  most 
important  progress),  by  Henschen,  et  al.  The  motor-oculi  nucleus  is  better  known 
since  the  labors  of  Gudden,  Perlia,  Westphal-Siemerling,  Bernheimer,  Kolliker,  and 
the  author. 

It  is  of  considerable  importance  to  know  what  to  regard  as  fairly  accurate 
signs  of  disease  of  the  quadrigeminal  region.  Disease-foci  in  the  regio  subthalamica 
encounter  such  a  tangle  of  various  fibers  that  the  resultant  symptoms  show  great 
diversity.  A  positive  diagnosis  could  scarcely  be  possible. 

Lesions  in  the  cerebral  peduncle  intercept  the  motor  fibers  to  the  opposite 
half  of  the  body  and  head.  There  may  be  added  sensory  and  vasomotor  disturbances. 
Usually,  however,  not  only  paralysis  of  the  opposite  extremities  and  of  one  or  several 
cranial  nerves  results,  but  also  weakness  of  the  motor-oculi  of  the  same  side.  When 
simultaneous  paralysis  of  one  oculo-motorius  and  of  the  opposite  half  of  the  body 
exists,  one  may  suspect  a  lesion  below  the  corpora  quadrigemina.  Such  patients  move 
the  limbs  of  one  side  feebly  or  not  at  all,  while  on  the  opposite  side  there  are  ptosis, 
dilatation  of  the  pupil,  and  abduction  of  the  eyeball.  A  basal  tumor  may  produce 
the  same  symptoms  (Cf.  Fig.  237);  it  is,  therefore,  diagnostically  important,  when 
paralysis  of  the  ocular  muscles  and  that  of  the  extremities  appear  together,  which 
could  only  arise  (as  in  the  last-mentioned  case)  through  a  peculiar  combination  of 
circumstances.  When  anaesthesia  is  present,  it  is  likewise  confined  to  the  opposite 
side  of  the  body.  The  sensory  fibers  probably  course  in  the  fillet. 

If  the  disease-focus  extends  farther  dorsally,  reaching  the  corpora  quadrigemina 
themselves,  there  ensues  naturally,  besides  the  unilateral  or  bilateral  oculo-motor 
paralysis  of  disease  of  the  anterior  quadrigeminal  bodies,  also  visual  disturbance; 
occasionally  nothing  abnormal  can  be  found  ophthalmoscopically.  With  tumors 
here,  as  elsewhere  in  the  brain,  there  may  follow  choked  disk,  optic  atrophy,  etc. 
Usually  pupillary  reaction  is  lost. 

The  symptoms  of  disease  of  the  posterior  quadrigeminal  bodies  are  not  known. 
Disturbances  of  equilibrium  and  co-ordination  have  accompanied  it. 

Disease  of  the  quadrigeminal  region  may  be  suspected  when  paralysis  of  both 
motor  oculi  is  present  without  peripheral  (i.e.,  basal)  cause,  or  when  only  a  portion 
of  one  motor  oculi  is  injured  (e.g.,  only  the  fibers  to  the  internal  rectus).  Lesions 
of  the  peripheral  trunk  could  scarcely  produce  this,  such  paralysis  being  nearly 
always  nuclear  in  its  origin. 


CHAPTEK    XX. 
THE   PONS  AND  THE   CEREBELLUM. 

IT  was  learned  in  the  foregoing  chapter  that  the  bundles  of  fibers  from 
the  cerebrum  and  the  thalamencephalon1  are,  in  the  region  of  the  mesen- 
cephalon,  arranged  in  two  different  layers:  the  pes  pedunculi  and  the  teg- 
mentum.  Posterior  to  the  corpora  quadrigemina  the  aquaeductus  becomes 
much  widened.  The  pes  and  the  tegmentum  pass  under  it  farther  down- 
ward into  the  metencephalon.  Only  one  constituent  of  the  tegmentum, 
the  anterior  peduncle  of  the  cerebellum,  which  originates  in  the  red  nucleus, 


Fig.  200. — The  pedunculus  cerebri  and  the  pons  as  seen  anteriorly.  The 
tract  of  pedal  fibers,  which  does  not  terminate  in  the  pons,  is  shaded.  Him- 
shenkel,  Pedunculus  cerebri.  Kleinhirn,  Cerebellum. 

passes  now  from  the  floor  of  the  mesencephalon  dorsally  to  the  roof  of  the 
metencephalon.  This  roof  develops  into  the  cerebellum.  That  portion  of 
the  central  canal  which  lies  under  it  is  the  continuation  of  the  aqueduct 
and  is  called  the  fourth  ventricle.  The  floor  and  lateral  portions  of  the 
metencephalon  contain  the  continuation  of  the  pes  and  tegmentum. 

Note  first  what  becomes  of  the  fibers  of  the  pes:    Not  far  posterior  to 


1  See  also  Chapters  XVI  and  XVII. 
(310) 


THE    POXS   AND   THE    CEREBELLUM.  311 

the  corpora  quadrigemina  a  thick  white  mass  of  fibers  lies  ventral  to  the 
cerebral  peduncles.  Descending  from  the  cerebellum,  they  embrace  and 
cover  the  pedal  region  in  a  thick  layer.  These  fibers  taken  together  are 
called  the  pons. 

Only  a  part  of  the  fibers  cover  the  crusta  externally, — stratum  super- 
ficiale  pontis, — most  of  them  invade,  from  both  sides,  the  fiber-system  of  the 
crusta,  dividing  it  into  isolated  fasciculi:  stratum  compkxum  et  profundum 
pontis. 

It  will  be  remembered  that  of  the  fibers  which  pass  ventrally  into  the 
crusta  from  the  cerebrum  only  a  portion  can  be  followed  as  far  as  the  pons. 
These  were  the  fasciculi  from  the  frontal,  parietal,  and  temporal  lobes.  The 
pyramidal  tract,  from  the  region  of  the  central  convolutions,  passes  through 
the  pons.  Almost  the  whole  inner  third  and  the  whole  outer  third  of 
the  crusta  terminate  in  the  pons.  Beyond  the  latter  only  the  middle  third 
of  the  pes — namely,  the  pyramidal  tract — passes  out  (see  Fig.  200). 

The  fibers  of  the  pons  come  from  above  out  of  the  cerebellar  hemi- 
spheres, embrace  and  penetrate  the  fibers  of  the  pes  and  in  the  more  ventral 
regions, — stratum  superficial,— terminate,  for  the  most  part,  in  the  pontal 
ganglia  of  the  same  side;  while,  in  the  more  dorsal  regions,  in  those  of  the 
opposite  side  (Minghazzini).  The  pontal  ganglia  are  gray  masses  filled  with 
a  reticulum  of  fine  fibers,  in  which  one  may  follow  both  the  fibers  from  the 
arms  of  the  pons  (brachia  pontis)  and  the  tracts  whieh  arise  from  the  cere- 
brum. 

Through  the  investigations  of  S.  R.  y  Cajal  it  has  become  quite  certain  that 
the  strong  cortico-pontal  fasciculi  ramify  around  the  large  cells  of  the  pontal  ganglia, 
and  that  the  arms  to  the  cerebellum  are  formed  from  the  neuraxons  of  those  cells. 
But  experiments  show,  also,  that  a  part  of  the  pontal  fibers  degenerates  after  ex- 
tirpation of  the  cerebellum.  We  must,  therefore,  conclude  that,  as  in  many  other 
bundles,  so  in  the  arms  of  the  pons  there  are  fibers  which  pass  in  both  directions, 
namely:  fibers  from  the  cells  of  the  cerebellum  to  the  pontal  ganglia,  and  fibers  from 
the  ganglia  to  the  cerebellum. 

In  animals  with  a  relatively  small  cerebrum  the  pons  is  also  small.  Compare 
Fig.  141  with  Fig.  180.  Here  in  the  calf  there  is  seen  a  transverse  system  of  fibers, 
corpus  trapezoides,  lying  between  the  pedal  and  tegmental  portions  of  the  pons:  a 
system  of  fibers  which,  in  man,  is  covered  by  pontal  fibers.  It  contains  the  fasciculi 
which  belong  to  the  acusticus. 

In  mammals  there  is  added  to  the  pontal  fibers  that  tract  from  the 
cerebellum  to  the  tegmentum  of  the  medulla  which  was  demonstrated  during 
the  consideration  of  the  brain  of  the  lowest  vertebrates.  The  fibers  of  this 
tract  do  not  pass  into  the  pontal  ganglia,  but  diverge  from  their  course, 
decussating  dorsally  in  the  raphe  of  the  pons,  and  are  lost  in  the  gray 
matter  of  the  tegmentum  (see  Fig.  2016). 

The  pes  pedunculi  is  split  up  by  the  pontal  system  of  fibers  and  in  part 


312 


ANATOMY    OF    THE    CENTRAL    NERVOUS    SYSTEM. 


diverted  to  the  cerebellum;   the  tegmentum,  however,  passes  through  the 
pontal  region  only  slightly  changed. 

In  the  last  cross-section  through  the  region  of  the  corpora  quadrigemina 
(Fig.  199)  we  had  the  following  essential  constituents  of  the  tegmentum: — 

1.  The  gray  substance  about  the  aqueduct,  together  with  the  nuclei  of 
its  nerves. 

2.  Below  it  the  post.  long,  fasciculus. 

3.  Outside  the  latter  are  the  fibers  of  the  commissura  posterior. 


Corpus  quadr.  post 


Aquaeductus  Sylv. 


Nuc.  N.  trochl. . 

Nucleus  laqn.. 

Fasc.  long.  post. . 

Sutst.  ret.  Tr.tlial.  bulb.. 
Cerebellar  peduncle 


Median  (sup.)  fillet 
Fasc.  from  pes  to  tegmentum 

Raphe.    Deeussation  1 

of  peduncles        fi 
Corpus  interpedunculare 

Tr.  mamillo-peduncular. 


Fig.  201. — a  and  6,  Two  sections  through  the  most  anterior  portion  of  the 
pons.  Fig.  201  a  shows  the  corp.  quadr.  post.,  ventral  to  which  are  the  nucleus 
of  the  trochlearis  and  the  decussation  of  the  anterior  cerebellar  peduncles.  Ven- 
trally  one  sees  on  the  left  diagrammatically  outlined  the  pes  pedunculi  which,  on 
the  right,  is  shown  to  be  traversed  by  pontal  fibers. 


4.  The  fibers  from  the  striae  medullares  thalami. 

5.  The  red  nuclei  in  the  center  of  the  tegmentum,  and  the  cerebellar 
peduncles  arising  from  them. 

6.  The  fillet. 

7.  The  Pedunculus  corporis  mamillaris. 

8.  Fibers  from  the  deep  medullary  stratum  near  the  median  line. 


THE  POXS  AND  THE  CEREBELLUM. 


313 


As  stated  above,  the  aqueduct  widens  out  into  the  fossa  rhomb oidalis; 
and  the  surrounding  gray  substance  also  increases  in  area.  A  new  nucleus, 
nucleus  n.  trochlearis,  is  found  below  the  corp.  quad.  post.  The  fibers  of 
the  Trochlearis  do  not,  however,  like  the  fibers  of  the  oculo-motorius,  pass 
downward  through  the  tegmentum,  but  pass  backward  immediately  after 
their  origin  in  nearly  horizontal  direction,  then  rise  and  decussate  finally, 
in  the  velum  medullare  anticum,  with  those  of  the  opposite  side.  They  thus 
leave  the  brain  on  the  dorsal  side  just  posterior  to  the  corp.  quad.  post.  In 
Figs.  201a  and  201&  portions  of  the  course  of  the  trochlearis  are  visible. 
In  Fig.  196  the  whole  course  of  the  nerve  is  depicted. 

The  posterior  longitudinal  fasciculi  and  the  fibers  of  the  posterior  com- 
missure, retaining  the  same  relation  as  in  the  midbrain,  pass  down  into  the 


Decuismtiuu  of  the  troelilearis 

Had.  meseoceph.  N.  trig. 

Nucl.  laquearis 

Fase.  long.  post. 

Cerebellar  peduncle 

Fasc.  from  the  tegmental  decussation 

Lat.  fillet 

Fasc.  farm  pons  to  tegmentum 
Median  fillets- 


Fig.  201&  shows  clearly  the  changes  in  the  tegmentum  which  occur  just 
posterior  to  the  corpora  quadrigemina.  Note  also  the  decussation  of  the  troch- 
learis. Compare  in  the  two  sections  the  corresponding  fasciculi. 


tegmentum  of  the  medulla.  The  same  is  true  of  the  stratum  lemnisci.  To 
the  latter  new  fibers  are  added  from  the  lateral  margin  of  the  corp.  quad, 
post.  They  lie  outside  of  the  horizontal  layer  formed  by  the  upper  and 
lower  fillets  and  are  usually  designated  as  the  lateral  fillet  (lemniscus  later- 
ale)  to  distinguish  them  from  the  former  or  median  fillet  (lemniscus 
mediale).  The  lateral  fillet  from  the  posterior  quadrigeminal  body  goes 
almost  exclusively  to  the  termini  of  the  auditory  nerve.  In  them  lie  groups 
of  ganglion-cells, — nucleus  laquearis, — the  neuraxons  of  which  mostly  join 
the  ascending  and  descending  fillets. 

In  Fig.  202  one  sees  above  and  externally  the  triangular  lateral  fillet 
passing  downward  to  the  horizontal  median  fillet. 


314 


ANATOMY    OF    THE    CENTRAL    NERVOUS    SYSTEM. 


The  Substantia  nigra,  and  with  it  the  stratum  intermedium,  do  not  ap- 
pear in  sections  in  the  region  of  the  pons.  Of  the  continuation  of  the  striae 
medullares  thalami  nothing  is  known  with  certainty. 

Even  before  the  pontal  region  begins,  the  red  nucleus  always  becomes 
smaller,  and  the  anterior  cerebellar  peduncle,  which  arises  from  it,  passes 
farther  and  farther  to  the  outside,  and  finally  appears  as  two  strong  bundles 
of  fibers  which  lie  between  the  region  of  the  red  nucleus  and  the  fillet.  In 
Fig.  201a  the  fundament  of  the  cerebellar  peduncle  appears;  in  sections 
which,  falling  slightly  posterior  to  this,  cut  the  velum,  the  peduncles  lie 


Fig.  202. — Section  through  the  upper  pontal  region  just  posterior  to  the 
corpora  quadrigemina.  From  a  ninth-month  fetus.  Bindearm,  Anterior  cere- 
bellar peduncle.  Brticke,  Pons.  Schleife,  Fillet.  Hint.  Liingsbundel,  Post.  long, 
fascic. 


much  nearer  to  the  periphery  (Fig.  201&);  and  in  Fig.  202  they  form, 
through  the  velum  medullare  posticum,  the  outer  boundary  of  the  figure. 
Soon  afterward  they  sink  into  the  cerebellum  (Fig.  210,  R). 

The  region  which  is  left  free  through  the  disappearance  of  the  red 
nucleus  is  appropriated  by  the  now  increasing  fibers  of  the  substantia  reticu- 
laris,  which  will  be  studied  later.  These  are  fibers,  mostly  longitudinal, 
which  may  be  followed  from  the  lowest  levels  of  the  oblongata  in  gradually 


THE  PONS  AND  THE  CEREBELLUM.  315 

decreasing  mass  up  to  the  midbrain  and  beyond  to  the  most  ventral  region 
of  the  thalamus.  They  arise  from  cells  which  lie  at  the  posterior  end  of 
the  tract  and  from  cells  located  along  the  course.  In  a  dog  lacking  a  thala- 
mus they  were  intact.  We  have  to  do  here,  probably,  with  a  system  which 
joins  together  different  levels  of  the  tegmentum. 

It  is  not  difficult,  if  one  has  once  thoroughly  understood  the  significance 
of  the  separate  fields  of  a  good  section  through  the  corpora  quadrigemina, 
to  find  the  same  in  sections  through  the  upper  part  of  the  pons  and  to 
interpret  them  rightly.  The  changes  concern,  in  general,  only  the  location 
•of  the  cerebellar  peduncle  and  the  conformation  of  the  gray  substance  under 
the  widening  aqueduct  where  new  nerve-nuclei  arise;  then  the  accession  of 
the  lateral  fillet  to  the  stratum  lemnisci  and  the  increase  of  the  systems  of 
the  substantia  reticularis. 

But  when  one  makes  cross-sections  farther  back  the  picture  is  essen- 
tially modified.  This  occurs  through  the  formation  of  the  cerebellum  from 
the  roof  of  the  ventricle  posterior  to  the  velum  medullare  anticum,  and 
through  the  intimate  relation  into  which  the  cerebellum  enters  with  fibers 
from  the  tegmentum  and  from  the  pes. 

Cerebellar  peduncles  and  pontal  arms  disappear  in  the  cerebellum. 
From  the  medulla  and  spinal  cord  come  fibers  which  are  interwoven  with 
those  of  the  tegmentum  and  turn  also  to  the  cerebellum. 

It  is  therefore  advisable  to  leave  for  a  time  the  tracing  of  the  tegmen- 
tal  tract  and  pass  to  the  study  of  those  parts  of  the  central  nervous  system 
into  which  the  tracts  disappear.  The  picture  of  the  tegmental  system  will 
doubtless  be  much  more  easily  comprehensible  after  the  reader  has  become 
somewhat  familiar  with  the  arrangement  of  fibers  in  the  cerebellum,  and 
after  he  has  learned  to  know  the  structure  of  the  spinal  cord  and  the  medulla 
oblongata. 


THE  CEREBELLUM. 

The  cerebellum  consists  of  a  middle  portion,  the  vermis,  and  the  two 
hemispheres.  It  is  in  connection  with  the  thalamus  anteriorly  through  an- 
terior cerebellar  peduncles  from  the  nucleus  ruber,  and  with  the  cerebrum 
ventrally  through  the  brachia  pontis,  the  middle  cerebellar  peduncles. 
Through  the  first  it  receives  principally  fibers  from  the  thalamus  and  from 
the  region  of  the  tegmental  radiation;  through  the  second  bundles  from  the 
cortex  of  the  frontal,  parietal,  and  temporal  lobes.  A  third  connection  binds 
the  cerebellum  to  the  medulla  oblongata  and  the  spinal  cord  through  the 
posterior  cerebellar  peduncles — the  corpora  restiformia. 

In  the  following  figure,  which  shows  the  cerebellum  from  above, 
one  may  note: — 


316 


ANATOMY    OF    THE    CENTRAL    NERVOUS    SYSTEM. 


1.  The  position  with  reference  to  the  corpora  quadrigemina,  from 
beneath  which  the  anterior  cerebellar  peduncles  pass  to  the  cerebellum. 

2.  The  general  conformation,  with  the  vermis  in  the  middle  and  the 
hemispheres  are  subdivided  into  separate  rather  large  lobes.    Those  of  the 
vermis  are  arranged  about  the  medullary  portion  in  a  position  simulating 
the  blades  of  a  ship's  propeller  (see  Fig.  206). 

The  vermis  is  connected  on  the  right  and  left  with  the  white  substance 
of  the  cerebellar  hemispheres,  which  are  divided  into  lobes  by  deep  fissures 
and  into  ridges  by  shallow  ones. 


Fig.  203. — The  cerebellum.     (Dorsal  aspect.) 


The  dorsal  surface  of  the  vermis  is  called  the  superior  vermiform  proc- 
ess.   It  is  divided  into: — 

(A)  Lingula,  far  forward  between  the  peduncles. 

(B)  Lobulus  ceniralis,  passing  into  the  alas  lobuli  centralis  on  each  side. 

(C)  Monticulus,  or  mount,  of  which  the  anterior  part  is  called  the  culm 
and  the  posterior  part  the  declivity. 

(D)  Folium  vermis,  or  fol.  cacuminis,  at  the  posterior  end  of  the  supe- 
rior vermiform  process. 

(E)  Tuber  vermis,  or  tuber  valvulas. 


THE    POXS    AND    THE    CEREBELLUM. 


317 


Upon  the  dorsal  aspect  of  the  hemispheres  may  be  differentiated: — 

1.  Lobus  quadrangular  is  or  anterior  upper  lobe  on  either  side  of  the 
monticulus. 

2.  Lobus  semilunaris  superior  or  posterior  upper  lobe.     The  two  pos- 
terior upper  lobes  are  connected  by  the  folium  cacuminis. 

The  lobes  of  the  under  surface  of  the  cerebellum  are  shown  in  the  next 
figure  (204).  It  presents  a  rather  complicated  picture.  In  order  to  prepare 
specimens  for  this  view  the  cerebellum  must  be  severed  from  its  connection 
with  the  midbrain, — i.e.,  the  anterior  cerebellar  peduncles  must  be  severed, 
— then  from  its  connections  with  the  pons  and  with  the  medulla  and  cord. 
Thus  on  each  side  there  are  the  three  cross-sections  of  the  cerebellar 
peduncles.  Between  the  anterior  cerebellar  peduncles  lies  a  thin  membrane, 


Fig.  204. — The  cerebellum.     (Ventral  aspect.) 


the  velum  medullare  anticum,  which  is  a  part  of  the  roof  of  the  meten- 
cephalon.    The  cut  surface  of  it  is  to  be  seen  in  the  figure. 

The  lobes  on  the  ventral  surface  of  the  vermis  are  called: — 

1.  Nodulus. 

2.  Uvula. 

3.  Pyramis. 

4.  Tuber  valvulce,  making  the  boundary  between  the  ventral  and  dorsal 
surface  of  the  vermis  (see  Fig.  203). 

The  lobes  on  the  ventral  surface  of  the  hemispheres  are: — 

1.  Flocculus,  on  each  side  of  the  nodulus  and  moored  by  the  slender 
pedunculus  ftocculi. 

2.  Tonsilla,  on  either  side  of  the  uvula. 


318  ANATOMY    OF    THE    CENTRAL    NERVOUS    SYSTEM. 

3.  Lobus  cuneiformis,  lying  external  to  the  tonsilla. 

4.  Lobus  posterior  inferior,  the  anterior  portion  of  which  is  called  the 
lobus  gracilis  and  the  posterior  portion  the  lobus  semilunaris  inferior. 

In  Fig.  205  one  may  see  on  either  side  the  three  medullary  processes, 
or  commissures,  which  pass  to  the  cerebellum.  The  fibers  of  these  commis- 
sures pass  into  the  central  white  substance  of  the  hemispheres,  thence  into 
the  medullary  portion  of  the  individual  lobes,  whence  they  extend  into  the 
lobules  and  ridges.  These  ridges  are  covered  with  gray  cortex  which  every- 
where follows  the  conformation  of  the  medullary  substance  and  thus  gains 
an  extension  which  is  greater  than  the  outer  form  and  size  of  the  cerebellum 
would  lead  one  to  expect. 

The  white  substance  of  the  hemispheres  is  considerable  in  quantity. 


Fig.  205. — The  three  pairs  of  cerebellar  peduncles.  8,  Corpora  quadri- 
gemina.  5,  Anterior  cerebellar  peduncle.  7,  Middle  cerebellar  peduncle,  or 
Brachium  pontis.  3,  Posterior  cerebellar  peduncle.  1,  Fossa  rhomboidalis.  2, 
Stria;  acustioe.  6,  Fillet.  (After  Hirschfeld  and  Leveille.) 

The  accompanying  sagittal  section  of  the  cerebellum  passes  through  the 
center  of  the  vermis  (Fig.  206).  It  shows  how  the  medullary  substance  is 
continuous  anteriorly  with  the  velum  medullare  anticum,  which  extends  as 
a  thin  membrane  toward  the  corpora  quadrigemina.  This  thin  membrane, 
stretched  between  the  anterior  peduncles,  forms  a  transition  from  the  roof  of 
the  mesencephalon  to  the  roof  of  the  metencephalon.  Upon  it  lies  the 
most  anterior  lobule  of  the  superior  vermiform  process:  the  lingula. 

The  peculiar  picture  presented  by  the  longitudinal  section  of  the  vermis 
has,  from  time  immemorial,  borne  the  name  arbor  vitce.  The  central  por- 
tion of  the  medullary  part  is  called  the  corpus  trapezoides.  Into  this  there 


THE  POXS  AXD  THE  CEREBELLUM. 


319 


pass  separately  the  lingula,  lobulus  centralis,  uvula,  and  nodulus.  A 
number  (five)  of  the  lobules  of  the  monticulus  are  united  with  the' vertical 
branch  (Vert.  A)  before  their  juncture  with  the  main  truck  of  the  arbor 
vita?.  The  posterior  portion  of  the  monticulus,  together  with  the  folium 
cacuminis  and  the  tuber  valvulaa,  unite  to  form  the  horizontal  branch  (Horiz. 
A)  of  the  arbor  vita?. 

Posteriorly  the  velum  medullare  posticum  passes  from  the  cerebellum 
as  roof  of  the  fossa  rhomboidalis  as  far  as  to  the  termination  of  the  posterior 
column  of  the  spinal  cord.  This  roof  consists  only  in  its  lateral  portions  of 
rather  dense  tissue,  principally  neuroglia;  in  the  median  line  it  is  simply  a 
layer  of  cuboidal  epithelium.  From  the  pia  numerous  vascular  loops  pass 
into  this  membrane  and  press  it  somewhat  into  the  ventricle  (plexus 
chorioideus  ventriculi  quarti,  or  plex.  chor.  medialis).  But  the  most  later- 


Fig.  206. — Sagittal  section  through  the  middle  of  the  Vermis. 


ally  located  portions  of  the  membrane  form,  in  the  region  of  the  oblongata, 
sack-like  projections  whose  median  wall,  through  vascular  loops,  likewise 
becomes  a  choroid  plexus:  plexus  chorioideus  lateralis  (see  Fig.  243).  In 
the  median  as' well  as  in  the  place  of  origin  of  the  lateral  plexus  perforations 
are  found  (Key  and  Retzius).  The  middle  one  of  these  openings  is  called  the 
foramen  of  Majendie.  It  is  of  great  importance  in  the  ready  equalization 
and  adjustment  of  variations  of  pressure  in  the  cerebro-spinal  fluid. 

Into  the  cerebellum  pass  the  three  pairs  of  commissural  arms.  They 
pass  into  the  central  white  substance  and  form  connections  there  with  gray 
nuclei;  they  also  send. fasciculi  to  the  cortex  of  the  cerebellum. 

In  the  cortex  one  may  even  with  low  magnification  differentiate  three 
different  layers:  Externally  lies  the  zona  molecular  is;  internally  the  zona 
granulosa;  while  between  them  one  finds  a  layer  of  very  large  cells — the 
cells  of  Purkinje. 


320  ANATOMY   OF   THE    CENTRAL   NEEVOUS    SYSTEM. 

Eecall  that  in  Chapter  III  it  was  stated  that  according  to  recent  views 
the  connection  of  one  cell  to  another,  in  the  central  nervous  system,  is 
established  through  the  protoplasmic  processes  of  one  cell  being  surrounded 
by  the  terminal  ramifications  of  the  neuraxons  of  the  other.  Since  the  term 
neuron  includes  the  cell  and  its  protoplasmic  processes  with  the  neuraxon 
and  its  terminal  ramification,  one  may  say:  In  the  whole  nervous  system 
there  are  innumerable  separate  neurons  which  are  associated  together  in  the 
manner  described  above.  An  example  of  this  is  also  found  in  the  olfactory 
lobe.  In  the  minute  structure  of  the  cerebellum  we  may  verify  the  prin- 
ciple just  formulated. 

The  cells  of  Purkinje  (see  1  in  Fig.  207)  send  neuraxons  down  into  the 
zona  granulosa  and  into  the  medullary  layer  below  this.  On  the  way  they 
give  off  collaterals,  some  of  which  bend  around,  pass  upward,  and  break  up 
into  branches  around  the  body  of  the  cell.  The  dendritic  processes  are 
extraordinarily  profuse,  especially  in  the  sagittal  plane, — less  so  in  i^he 
transverse  plane.  If  one  wishes  to  get  such  a  view  as  is  shown  in  Fig.  207, 
the  sections  must  be  cut  transverse  to  the  fissures  of  the  cerebellum. 

The  profuse  dendritic  branches  are  now  interspersed  with  thick  fibers 
(see  2,  Fig.  207),  which,  coming  from  cells  of  unknown  location,  enter  the 
cerebellar  medulla,  traverse  the  zona  granulosa,  finally  breaking  up  into 
branches  in  the  zona  molecularis.  Thus,  every  cell  of  Purkinje  is  placed 
in  connection  with  a  distinct  locality.  But  there  is  a  kind  of  cell  in  the 
molecular  layer  which  is  adapted  to  bring  into  connection  with  each  other 
a  number  of  the  Purkinje  cells.  Such  cells  (see  3,  Fig.  207)  send  out,  nearly 
parallel  to  the  surface  of  the  cortex,  a  long  neuraxon,  which  gives  out  fine 
processes  at  intervals  along  its  course.  A  process  passes  to  the  body  of  one 
of  the  Purkinje  cells,  and  breaks  up  into  branches  around  it. 

The  granular  layer  consists,  for  the  most  part,  of  small  polygonal  cells 
with  large  nuclei  (see  4,  Fig.  207).  Each  one  of  these  cells  sends  out  a 
number  of  short  dendrites  and  a  neuraxon.  The  latter  passes  outward  into 
the  molecular  layer,  where  it  divides  into  two  fibers  which  are  transverse  to 
the  axis  of  the  body.  In  the  figure  this  division  is  indicated  by  a  short  trans- 
verse line  because  the  section  is  a  sagittal  one, — i.e.,  transverse  to  the  con- 
volutions of  the  cerebellum.  The  numerous  dots  scattered  over  the  molecu- 
lar layer  in  the  lower  right  hand  part  of  the  figure  represent  the  sections  of 
these  neuraxons.  Besides  the  cells  just  described,  there  are,  in  the  granular 
layer,  cells  whose  neuraxons  break  up  at  once  into  very  fine  twigs  which 
ramify  among  the  elements  of  the  granular  layer  and  whose  dendrites — not 
unlike  those  of  the  Purkinje  cells,  though  less  branched — are  distributed  to 
the  molecular  layer.  Furthermore,  there  end  in  the  granular  layer  fibers  of 
unknown  origin  which  enter  this  layer,  from  the  medullary  layer  (see  6. 
Fig.  207). 


THE  PONS  AND  THE  CEREBELLUM. 


321 


As  will  be  seen  from  this,  the  cortex  of  the  cerebellum  is  an  exceedingly 
complicated  apparatus,  an  apparatus  which  is  adapted  for  uniting  elements 
of  very  different  character  and  origin. 

In  the  section  presented  in  Fig.  208  one  may  note:  1.  That  the  fibers 
from  the  central  white  matter  of  the  cerebellum  pass  into  the  cortex  in 


Fig.  207. — Diagrammatic  sagittal  section  through  the  cerebellar  cortex.     Golgi 
method.     (After  drawings  by  S.  R.  y  Cajal  and  V.  Gehuchten.) 

thick  medullated  fasciculi.  2.  That  in  the  region  of  the  granular  layer 
only  curved  pieces  of  these  fibers  are  shown.  3.  That  these  form  a  true 
plexus  of  medullated  fibers  lying  in  the  sagittal  plane  below  and  between  the 
Purkinje  cells.  Running  in  the  same  direction  are  separate,  thin,  medullated 
fibers, — not  shown  in  the  figure, — which  lie  just  beyond  the  bodies  of  the 
Purkinje  cells  in  the  molecular  layer. 


322 


AXATOMY    OF    THE    CENTRAL    NERVOUS    SYSTEM. 


The  cortex  of  the  cerebellum  has  been  thus  described  in  detail  because 
recent  investigations  have  shown  that  in  progressive  paralysis  degeneration 
of  fibers  and  other  changes  may  take  place  here.  The  knowledge  of  the 
anatomical  relations  may  thus  become  of  great  importance  in  investigations 
in  the  realm  of  pathology. 

All  parts  of  the  cortex  are  connected  with  each  other  through  plaited 
fasciculi  which  conform  to  the  contour  of  the  cortex. 


Fig.  208. — Section  through  the  cortical  layer  of  the  cerebellum.  Heema- 
toxylin  staining.  Kornersctiicht,  Zona  granulosa.  Rinde,  Cortex.  Markleiste, 
Medullary  fascicle. 


The  cerebellum  presents  collections  of  gray  matter  besides  that  which 
is  in  the  cortex.  On  either  side  of  the  vermis  lies  a  large,  much-folded 
nucleus — corpus  dentatum.  On  the  median  side  of  this  other  gray  masses 
are  met:  first  the  Erribolus;  then  the  Nucleus  globosus,  an  elongated  struct- 
ure with  a  tuberosity  at  the  posterior  end;  and,  finally,  nearest  the  median 


THE    PONS    AND    THE    CEREBELLUM. 


323 


line  is  the  nucleus  tegmenti  (nuc.  fastigii).  These  nuclei  are  best  brought 
into  view  in  a  nearly-horizona]  section  through  the  cerebellum,  as  is  shown 
in  Fig.  209,  taken  from  Selling's  Atlas. 

In  such  a  section  one  may  note  in  the  middle  the  white  substance  of 
the  vermis  and  the  nucleus  tegmenti;  anterior  to  this  a  decussation,  the 
anterior  commissure  of  the  vermis.  To  the  right  and  left  lies  the  white 
matter  of  the  hemispheres,  in  which  may  be  seen  the  nuc.  globosus,  the 
embolus,  and  the  folded  medullary  lamina  of  the  nuc.  dentatus.  The  deep 
clefts  in  the  surface  correspond  to  the  fissures  between  the  lobes.  Between 


Fig.  209.— Horizontal  section  through  the  cerebellum.  The  section  passes 
through  the  region  under  the  corp.  quad.  (T)  then  through  the  ant.  cerebellar 
peduncles  (R),  and  between  these  through  the  lingula  (.4).  Above  this  lies  the 
nuc.  tegmenti  (m),  to  the  left  of  the  nuc.  globosus  (Ny.),  the  embolus  (Emb.),  and 
still  farther  to  the  side  within  the  hemisphere  the  corpus  dentatum  cerebelli  ( Cdc) . 
Com.,  Anterior  decussation-commissure.  Sem,  Fibrae  semicirculares.  (After  B. 
Stilling.) 

the  peduncles  (R  R)  upon  the  velum  medullare  anticum  lies  the  lingula 
(A),  cut  also  in  the  horizontal  plane. 

All  of  the  nuclei  here  seen  in  the  white  substance  are  connected  with 
each  other  through  bands  of  gray  matter.  Their  relation  to  the  fiber-system 
of  the  white  substance  is  almost  wholly  unknown. 

If  one  make  a  frontal  section  just  posterior  to  the  point  where  the 


324  ANATOMY    OF    THE    CENTRAL   NERVOUS    SYSTEM. 

• 

anterior  peduncles  enter  the  cerebellum,  one  will  find  dorsally  the  cerebel- 
lum, ventrally  the  pons  and  the  fibers  which  pass  from  it  on  both  sides  into 
the  hemispheres.  Between  the  cerebellum  and  the  tegmentum,  bounded  on 
either  side  by  the  divided  peduncles,  lies  the  fourth  ventricle,  which  is  the 
widened  continuation  of  the  aqueduct  of  Sylvius.  The  medullary  substance 
of  the  vermis  does  not  lie  in  the  "plane  of  the  section.  The  tegmentum  and 
the  pes,  the  latter  traversed  by  the  pontal  fibers,  lie  in  the  same  relative  posi- 
tions as  when  seen  in  sections  through  the  region  of  the  corpora  quadri- 
gemina. 

We  have  found  that  fibers  pass  through  the  three  pairs  of  peduncles 
into  the  cerebellum.    Their  course  within  the  cerebellum  is  still  very  imper- 


Fig.  210. — Frontal  cerebellar  section  just  anterior  to  the  culmen.  V,  Ven- 
triculus  quartus.  R,  Anterior  peduncle.  P,  Pons.  Zon,  Decussation-zone.  Cr., 
Fibers  from  corp.  rest,  passing  to  Scm,  the  librae  semicirculares.  (After  B. 
Stilling.) 

fectly  known,  notwithstanding  the  fact  that  Benedict  Stilling  has  devoted 
long  years  of  work  to  the  study. 

However,  the  work  of  the  last  few  years,  especially  that  directed  to  the 
tracing  of  degenerations  which  follow  a  total  or  partial  extirpation  of  the 
cerebellum,  has  furnished  a  large  number  of  important  facts  regarding  the 
topography.  So  it  is  at  last  possible  to  elucidate  the  origin  of  the  separate 
arms. 

The  diagram  given  in  Pig.  211  shows  upon  the  frontal  sections,  through 
those  portions  of  the  central  nervous  system  which  are  in  immediate  asso- 
ciation with  the  cerebellum,  the  most  important  facts  at  present  known 
regarding  the  connections  of  the  cerebellum. 


THE    PONS   AND    THE    CEREBELLUM. 


325 


According  to  B.  Stilling's  opinion,  all  of  the  peduncles  receive  fibers 
from  nearly  all  parts  of  the  cerebellum,  each  peduncle,  however,  receiving 
especially  numerous  fibers  from  a  particular  portion. 


Fig.  211.— Schema  showing  the  origin  and  course  of  the  fibers  of 
the  peduncles  of  the  cerebellum. 


326  ANATOMY   OF   THE    CENTRAL   NERVOUS    SYSTEM. 

Comparative  anatomy  and  experiments  in  degeneration  uniformly  show  that 
in  the  cerebellar  connections  one  must  sharply  differentiate  between  the  cortex  of 
the  hemispheres  and  the  cortex  of  the  vermis;  also  between  the  cerebellar  cortex 
and  the  ganglia.  On  comparative  anatomical  grounds  the  author  reckons  the  corpus 
dentatum  with  the  vermis.  Not  a  small  proportion  of  what  is  said  in  the  literature 
of  degeneration  on  atrophy  after  injury  of  the  hemispheres  refers  to  injuries  of  the 
lateral  portion  of  the  vermis. 

1.  In  the  first  place  it  may  be  determined  that  the  cerebral  connection — • 
first  developed  in  mammals — is  furnished  by  the  ~bracliia  pontis  and  is  ex- 
clusively with  the  hemispheres  of  the  cerebellum.    Whence  arises  the  ascending 
fascicle  which  traverses  the  pons  ending  in  the  tegmentum?    The  arms  of 
the  pons  contain  fibers  from  cells  of  the  intrapontal  ganglia:  the  same  cells 
with  which  the  numerous  collaterals  of  the  cerebro-pontal  tract  connect. 
S.  R.  y  Cajal  has  demonstrated  this.    Even  degenerations  of  long  standing 
involving  the  fibers  of  the  pes  do  not  cause  complete  degeneration  of  the 
pons.    The  fact  that  after  removal  of  a  cerebellar  hemisphere  a  large  part  of 
the  pons  remains  intact  indicates  that  the  fibers  in  question  arise  from  the 
pontal  ganglia  and  not  from  the  cerebellum.    But,  nevertheless,  the  dis- 
appearance of  a  considerable  number  of  fibers  after  the  operation  (Marchi, 
Minghazzini,  Ferrier,  and  Turner)  makes  it  presumable  that  at  least  some  of 
the  fibers  of  the  pons  arise  from  cells  of  the  cortex  of  the  cerebellum. 

2.  It  may  be  demonstrated  by  several  methods  that  the  anterior  cere- 
bellar peduncles  arise  from  the  nucleus  dentatus',   they  may  possibly  also  re- 
ceive fibers  from  the  neighboring  cortex.    Much  the  greater  part  of  the  fibers 
end  after  decussation  in  the  red  nucleus  of  the  tegmentum  beneath  the 
anterior  quadrigeminal  bodies.     A  smaller  part  of  the  fibers,  end  in  the 
nucleus  ruber  of  the  same  side  and  send  a  few  fibers  farther  forward  to  the 
ventral  region  of  the  thalamus.     (This  last  point  is,  however,  not  yet  fully 
established.)     Since  a  tract  from  the  caudal  portion  of  the  parietal  lobe 
ends  at  the  nucleus  ruber,  it  is  evident  that  there  exists  here  an  indirect 
cerebro-cerebellar  connection. 

3.  The  posterior  cerebellar  peduncles  are  very  much  more  complexly 
constructed.    In  order  to  make  their  formation  quite  clear  we  must  divide 
them  into  (I)  a  median  portion  having  connections  with  the  sensory  cranial 
nerves,  especially  the  acusticus,  and  into  (II)  the  corpus  restiforme  proper, 
conducting  fibers  from  the  opposite  olivary  body  and  from  the  spinal  cord. 

The  median  portion  and  the  tracts  to  the  spinal  cord  are  inherited  from 
remote  antiquity;  but  only  in  the  mammals  do  the  bundles  to  the  olivary 
bodies  become  well  marked. 

The  corpus  restiforme  ends  almost  exclusively  in  the  middle  portion 
(vermis)  of  the  cerebellum,  where  its  separate  fascicles  pass  to  different 
regions.  The  region  of  the  nucleus  tegmenti,  and  this  nucleus  itself,  is  the 
terminus  of  the  nucleo-cerebellar  apparatus. 


THE    POXS    AND    THE    CEREBELLUM. 


327 


In  the  cortex  of  the  vermis,  especially  in  the  dorsal  portion,  fibers  from 
the  spinal  cord  end. 

The  terminus  of  the  olivary  tract  remains  yet  to  be  determined. 

The  constituents  of  the  post,  cerebellar  peduncle,  or  the  corpus  resti- 
forme,  will  now  be  more  definitely  considered. 


Fig.  212. — Frontal  section  through  the  cerebellum  and  pons  of  a  fetus  of 
twenty-six  weeks.  All  medullated  fibers  are  stained  with  hsematoxylin.  N.  V., 
Tr.  nucleo-cerebellaris.  Aus  dem  Corpus  restif.,  From  the  corp.  restif.  Binde- 
arm,  Ant.  cerebel.  peduncle. 


THE    MEDIAN'    POKTIOX. 


The  fasciculi  from  the  cerebellum  to  the  sensory  nerves  and  their 
nuclei,  with  which  we  became  acquainted  in  fishes,  exist  also  in  mammals. 
The  author  formerly  believed  that  we  had  to  do  here  with  direct  bundles 


328  ANATOMY    OF   THE    CENTBAL   NEEVOUS    SYSTEM. 

to  the  nerve-trunks.  But  recently  doubt  has  arisen  regarding  it,  since  the 
tract  has  not  with  perfect  certainty  been  traced  beyond  the  nucleus.  At 
any  rate,  it  is  wiser  at  present  to  designate  the  system  as  tr.  cerebellaris 
acustici,  etc.,  and  not  as  the  direct  sensory  cerebellar  tract.  In  Fig.  212, 
from  a  seven-month  human  fetus,  the  reader  will  recognize  a  part  of  the 
tract  which  passes  into  the  N.  trigeminus. 

II.      THE    COEPUS    BESTIFOBME    PEOPEE. 

(a)  The  Tr.  cerebello-spinales.     These  tracts  are  much  better  known 
than  are  the  sensory  fasciculi  of  the  median  portion.    There  are  now  three 
of  the  tracts  known: — 

1.  One  of  these  is,  on  good  grounds,  looked  upon  as  the  secondary  con- 
tinuation of  posterior  root-fibers:    the  Tr.  cerebello-spinalis  dorsaliff,  or  the 
lateral  cerebellar  tract  from  the  vesicular  column  of  Clarke.    This  fascicle 
constitutes  the  major  portion  of  the  spinal  connection  and,  curving  mesially, 
inclosing  the  corpus  dentatum,  passes  to  the  cortex  of  the  superior  vermiform 
process. 

2.  The  Tr.  cerebello-spinalis  ventralis,  or  the  bundle  of  Gowers,  whose 
triangular  cross-section  may  be  seen  in  all  the  sections  shown  in  Fig.  211, 
though  its  entrance  into  the  cerebellum  is  not  shown  in  the  figure.    It  passes 
into  the  pontal  tegmentum  far  forward,  and,  in  the  region  of  exit  of  the 
Trochlearis,  turns  dorsally,  embracing,  within  the  Velum  anticum,  the  an- 
terior peduncle  which  leaves  the  cerebellum  at  this  point,  and  then  turns 
backward  into  the  cerebellum  (Auerbach,  Mott). 

3.  Only  recently  has  it  been  demonstrated  by  Monakow,  and  also  by 
Ferrier  and  Turner,  that  still  a  third  spinal  connection  exists.     There  are 
thick  fibers  from  a  large  nucleus  of  multipolar  cells,  which  lies  just  where 
the  posterior  peduncle  enters  the  cerebellum.     The  nucleus  is  called,  from 
its  discoverer,  Deiter's  nucleus.     If  it  is  destroyed,  the  descending  fibers 
which  arise  from  it  degenerate  as  far  down  as  the  region  of  the  lateral 
tracts  (shown  in  Fig.  211). 

(b)  The  Tr.  cerebello-olivares  represent  another  constituent  of  the  cor- 
pus restiforme.    Their  fibers  become,  in  later  stages  of  development,  medul- 
lated  like  the  other  fibers  of  the  posterior  peduncle.    They  degenerate  com- 
pletely when  the  hemispheres  are  removed.    The  whole  bundle  passes  from 
the  cerebellum  to  the  oblongata,  enters  this,  and  passes  transversely  across  it, 
dividing  into  numerous  diverging  fascicles,  Anally  finding  a  terminus  in  the 
opposite  oliva  inferior  (see  Fig.  211). 

The  neuroglia  of  the  cerebellum  next  to  the  ventricle — as  usual,  in  the  boundary 
of  the  central  cavities — forms  a  thick  net-work.  In  the  white  substance  it  is  devel- 
oped at  least  as  strongly  as  in  the  medullary  substance  generally;  but  in  the  zona 


THE  PONS  AND  THE  CEEEBELLUM.  329 

granulosa  it  is  completely  lacking  in  healthy  persons.  In  paralytics,  however,  Wei- 
gert,  on  whose  authority  these  statements  are  made,  found  a  very  marked  exuber- 
ance of  the  glia.  From  the  region  of  the  cells  of  Purkinje  to  the  innermost  layer  of 
the  zona  molecularis  lie  small  slender  plexuses,  while  within  the  molecular  layer 
itself  there  are  found  relatively  sparingly  thick  fibers,  which  extend  perpendicularly 
to  the  surface:  the  Bergmann-Deiter  fibers.  The  surface  of  the  normal  cerebellum 
lacks  the  superficial  glia-net  usually  present  on  the  surface  of  the  central  nervous 
system.  But  in  all  embryos — even  in  non-mammals — one  finds,  as  outermost  layer 
of  the  cerebellum,  one  or  more  strata  of  spheroidal  cells  which  are  later  lost. 

The  outer  surface  of  the  cerebellum  was  described  by  Malacarne,  Eeil, 
and  Burdach  as  we  know  it  to-day.  The  investigation  of  its  inner  structure 
was  accomplished  by  F.  Arnold,  Eeil,  Kolliker,  Meynert,  and  especially  by 
B.  Stilling.  More  recent  investigations  on  the  constitution  of  the  peduncles 
were  made  by  Bechterew,  Marchi,  Minghazzini,  Ferrier  and  Turner,  and 
by  Pellizzi.  On  the  cortex  of  the  cerebellum  there  is  a  voluminous  litera- 
ture to  which  especially  Purkinje,  Gerlach,  Kolliker,  F.  E.  Schultze,  Ober- 
.steiner,  and  Bevor  furnished  contributions.  But  only  through  the  studies  of 
Golgi,  Eamon  y  Cajal,  Kolliker,  and  Gehuchten  does  one  obtain  an  exact 
understanding  of  the  structure.  Here,  as  in  so  many  other  places,  the  im- 
provement of  the  technique  made  possible  an  advance  where  the  most  dili- 
gent simple  observations  would  have  revealed  little. 

Diseases  of  the  cerebellar  peduncles  alone  are  very  seldom  observed. 
Thus,  little  is  known  of  the  symptoms  which  are  to  be  expected  in  the  case  of 
.such  a  disease.  Gradual  destruction  of  one  brachium  pontis  may  apparently 
give  rise  to  no  symptoms.  In  diseases  which  produce  an  irritation — for 
•example,  hemorrhages  and  tumors — forced  movements  frequently  occur, 
such  as  rolling  from  side  to  side.  A  forced  position  of  the  trunk  or  of  the 
head  alone,  with  or  without  nystagmus,  has  been  observed  in  irritating 
•diseases  of  one  of  the  arms  of  the  pons. 

For  the  determination  of  the  symptoms  conditioned  upon  diseases  of 
the  cerebellum  we  are  guided  primarily  by  the  quite  frequent  tumors,  and 
secondarily  by  the  not  infrequent  abscesses  which  accompany  purulent 
inflammations  of  the  ear.  Hemorrhage,  softening,  arteriosclerosis,  and 
other  pathological  processes  occur  in  the  cerebellum;  but  these  diseases  -are 
either  very  infrequent  and  usually  not  confined  to  the  cerebellum,  or  they 
lead — as  is  the  case  of  hemorrhages — so  quickly  to  death  that  no  time 
is  offered  for  the  development  of  a  special  combination  of  cerebellar  symp- 
toms. In  the  case  of  tumors,  and,  in  a  somewhat  less  degree,  in  abscesses 
of  the  brain,  there  exists  simply  the  difficulty  that  we  are  not  justified  in 
attributing  all  of  the  symptoms  which  appear  directly  to  the  lesion  of  that 
part  of  the  brain  involved  in  the  tumor.  Besides  the  so-called  local  phe- 
nomena, the  tumor  nearly  always  induces  two  other  groups  of  symptoms: 


330  ANATOMY   OF   THE    CENTRAL   NERVOUS    SYSTEM. 

first  those  which  are  due  to  the  effect  of  the  tumor  upon  the  neighboring 
tissue;  and,  second,  those  which  are  due  to  general  brain-pressure.  We  must 
sharply  differentiate  these  three  groups:  (1)  local  symptoms,  (2)  "neighbor- 
hood-symptoms," and  (3)  general  symptoms.  Because  of  the  narrowness- 
of  the  room  beneath  the  tentorium  cerebelli,  the  last  two  groups  are  often 
especially  emphasized. 

As  symptoms  induced  through  affection  of  the  cerebellum  itself — i.e., 
local  symptoms — we  should  enumerate  the  following:  1.  The  so-called  cere- 
bellar ataxia,  which  is  almost  without  doubt  a  direct  focal  symptom  of  the 
vermis  only,  and  especially  of  its  posterior  half.  A  tumor  could  cause  the 
same  symptoms  if  it  be  located  in  a  hemisphere.  It  is  possible  for  the 
ataxia  to  be,  in  part,  conditioned  upon  a  weakness  of  the  trunk-musculature. 
2.  Attacks  of  dizziness, — of  real  vertigo, — which  are  of  especial  importance 
when  appearing  as  an  early  symptom.  3.  Possibly  a  kind  of  tremor  which 
is  midway  between  ataxia  and  "intentional  tremor,"  and  a  similar  disturb- 
ance of  speech;  these  symptoms  may,  however,  be  simply  due  to  the  effect  of 
a  tumor  upon  neighboring  tissue  ("neighborhood-symptoms").  The  cere- 
bellum does  not  appear  to  have  direct  relations  to  the  motor  functions  in  a 
higher  sense.  Further,  its  disease  does  not  cause  specific  psychic  disturb- 
ances. 

In  diseases  of  the  cerebellum  "neighborhood-symptoms"  occur  espe- 
cially through  affection  of  the  pons,  the  medulla,  and  the  corpora  quad- 
rigemina. 

In  the  medulla  oblongata  and  in  the  pons  the  extramedullary  roots  or 
the  medullary  substance  itself  may  be  affected;  later  both  are  affected  to- 
gether. Especially  important  symptoms  here'are  alternating  hemiplegia  and 
possibly  hemianesthesia,  affecting  the  facialis  and  abducens  on  the  side  of 
the  tumor,  the  extremities  on  the  opposite  side,  or  disturbance  of  vision  on 
the  side  of  the  tumor.  The  extremities,  however,  may  be  affected  upon  the 
side  of  the  tumor  or  upon  the  opposite  side,  depending  upon  whether  the 
tumor  exerts  its  influence  above  the  decussation  of  the  pyramid  or  below  it. 
The  sudden  death  which  is  common  in  cerebellar  diseases  is  probably  a 
"neighborhood-symptom"  on  the  part  of  the  medulla  oblongata.  The  first 
symptom  manifested  by  the  extramedullary  nerves  is  frequently  neuralgia 
of  the  trigeminus. 

Neighborhood-symptoms  on  the  part  of  the  corpora  quadrigemina  are 
bilateral  ophthalmoplegias  which  affect  mostly  the  outer  branches  of  the 
oculo-motorius  and  the  trochlearis,  leaving  the  internal  recti  and  the  abdu- 
cens free.  These  symptoms  are  very  common  with  cerebellar  tumors. 

Prominent  symptoms  on  the  part  of  the  cerebellar  peduncles  with 
tumors  of  the  cerebellum  proper  are  rare;  they  are  described  above. 

The  general  symptoms  are  the  same  as  those  with  other  brain-tumors 


THE  PONS  AXD  THE  CEREBELLUM.  331 

They  are  characterized  only  through  especial  intensity.  Among  the  symp- 
toms are:  Choked  disk,  which  frequently  leads  to  blindness;  headache, 
especially  in  the  back  part  of  the  head  and  frequently  accompanied  by  stiff 
neck;  obstinate  emesis;  convulsions,  usually  tonic  and  with  opisthotonos. 

When  the  symptoms  are  pronounced  the  diagnosis  is  usually  easy. 
The  "neighborhood-symptoms"  are,  through  iheir  significance,  of  great 
importance.  In  order  to  establish  the  diagnosis  of  cerebellar  disease  the 
local  symptoms  must  naturally  precede  the  "neighborhood-symptoms." 
The  last  alone  not  infrequently  permit  a  diagnosis  of  the  side  of  the  cere- 
bellum diseased. 

Diseases  of  the  corpora  quadrigemina  may  give  rise  to  the  same  phe- 
nomena as  those  caused  by  diseases  of  the  cerebellum.  Here  ataxia  occurs 
only  after  ophthalmoplegia — the  reverse  of  the  case  with  affections  of  the 
cerebellum.  An  ataxia  due  to  affections  of  the  cerebrum  may  be  quite  like 
the  cerebellar  ataxia;  here  the  other  symptoms  indicate  disease  of  a  cerebral 
hemisphere  (Bruns). 


CHAPTEE    XXI. 

THE  PERIPHERAL-NERVE  BOOTS,  THE  SPINAL  GANGLIA,  AND  THE 
SPINAL  COED. 

THE  peripheral  nerves,  as  is  well  known,  contain  both  motor  and  sen- 
sory fibers.  Near  to  the  spinal  cord  these  separate  from  each  other.  The 
motor  division  enters  the  cord  directly  as  the  anterior  root.  The  sensory 
fibers  enter  the  spinal  ganglion. 

In  the  spinal  ganglia  .there  are  large  cells,  which  sometimes  give  off 
two  processes,  but  usually  only  one.  If  there  is  but  one,  it  divides  soon  after 


Vord 
.\Vurrel 


Nerv, 


Fig.  213.  —  Scheme  of  the  relationships  between  the  spinal  cord  and  the 
nerve-roots.  Vordere  Wurzel,  Anterior  root.  Hint.  Wurzel,  Posterior  root.  Mot. 
Theil,  Motor  portion.  Sens.  Theil,  Sensory  portion.  Gemischter  Nerv.,  Mixed 
nerve. 


leaving  the  cell-body  into  two;  so  that,  in  the  end,  it  amounts  to  practically 
two  cell-processes. 

It  will  be  remembered  that,  according  to  the  observations  of  His,  the 
sensory  nerves  grow  out  from  these  cells  as  peripheral  processes.,  but  that 
these  cells  also  send  one  process  into  the  spinal  cord,  a  bundle  of  such  proc- 
esses constituting  the  posterior  root. 

Since,  according  to  actual  count,  the  posterior  roots  contain  approxi- 
mately the  same  number  of  fibers  in  the  adult  as  the  nerves  just  beyond  the 
ganglia,  it  would  seem  that  there  were  simply  an  interposition  of  a  cell  in  the 
course  of  every  such  fiber. 

(332) 


PERIPHERAL-NERVE    ROOTS,    SPINAL    GANGLIA,    SPINAL    CORD.          333 

It  is  an  important  question,  however,  whether,  in  reality,  all  sensory 
nerves  arise  from  cells  in  the  spinal  ganglia.  The  experiment  of  Waller, 
since  oftentime^  successfully  repeated,  answers  it  completely. 

Every  nerve-fibre,  separated  from  ifs  source,  degenerates.  If  one  cut  the  fibers 
of  a  sensory  nerve  across,  just  peripheral  to  the  spinal  ganglion,  all  its  fibers  de- 
generate, while  the  ganglion  itself  and  the  fibers  leaving  it  to  form  the  corresponding 
root  of  the  cord  remain  fairly  normal.  This  shows  that  all  the  fibers  have  been 
divided  from  their  cells.  If  the  section  be  made  of  the  root  close  to  the  ganglion, 
but  few  of  the  fibers  in  the  sensory  nerve  die;  the  majority  retain  their  vitality. 
These  fibers  must,  therefore,  spring  from  the  cells  of  the  ganglion,  for  they  remain 
in  connection  with  them.  The  few  fibers  of  the  nerve  which  have  degenerated  must 
arise  in  the  cord  itself,  because  separated  from  it  alone,  and  not  from  the  ganglion. 


Fig.  214. — Scheme  of  the  fibers  in  a  spinal  ganglion.     Hintere  Wurzel, 
Posterior  root.    Sens.  Nerv.,  Sensory  nerve. 

In  fact,  examination  of  the  spinal  root  furnishes  the  proof  of  this.  The  root,  being 
separated  from  its  ganglion,  is  found  to  contain  only  a  few  living  fibers,  the  ma- 
jority being  degenerated.  The  intact  fibers  must  arise  from  cells  in  the  cord,  as 
they  remain  in  connection  with  such  cells  only;  the  degenerated  fibers  must  come 
from  the  ganglion,  because  they  are  divided  only  from  it.  ( Cf.  the  text  on  pages 
6  and  7.) 

These  experiments  show  that  from  the  ganglion-cell  processes  pass  in 
two  directions,  and  that  there  are  other  processes  from  the  cord  which  only 
pass  through  the  ganglion.  Probably  there  are  still  other  fibers  from  pe- 
ripheral (sympathetic)  cells  which  end  in  the  cord  (Fig.  33).  Accordingly 
one  may  consider  the  relations  of  the  sensory  roots  to  the  spinal  ganglia 
much  as  represented  in  Fig.  214. 


334  ANATOMY    OF    THE    CENTBAL   NEEVOUS    SYSTEM. 

Between  the  spinal  ganglion  and  the  spinal  cord  both  the  sensory  and 
the  motor  roots  break  up  into  smaller  fasciculi, — "root-fibers," — which  enter 
the  cord  at  considerably  various  levels,  the  sensory  fibers  posteriorly,  the 
motor  ones  anteriorly,  each  in  a  somewhat  laterally  placed  longitudinal 
sulcus.  The  number  of  these  fasciculi  is  not  the  same  for  different  roots, 
and  varies  also  in  different  individuals. 

Eecent  investigations  have  shown  that  for  the  extremities  not  every 
spinal  root  is  in  relation  to  a  particular  peripheral  nerve.  It  is  established 
that  in  every  nerve  going  to  one  of  the  extremities,  are  contained  a  large 
number  of  fibers  coming  from  different  spinal  roots,  and  it  is  very  probable 
that  two  muscles,  functioning  usually  co-ordinately,  are  innervated  from 
the  same  root,  even  when  supplied  by  different  nerves.  The  apportionment 
of  fibers,  which  renders  this  possible,  takes  place  partly  in  the  plexuses  (cer- 
vical, lumbar,  etc.),  and  in  part  in  the  trunks  of  the  larger  nerves,  which 
may  themselves  be  regarded  as  a  kind  of  plexus. 

Only  a  few  cases  of  disease  of  the  spinal  ganglia  are  reported.  Besides  ex- 
treme pain,  an  intercostal  herpes  zoster  in  the  course  of  the  respective  nerve  was 
repeatedly  observed.  Physiological  observations  (Gaule)  indicate  that  vasomotor  and 
trophic  influences  on  the  skin  and  muscles  are  the  province  of  some  of  the  cells  in 
the  spinal  ganglia.  Perhaps,  in  this  connection,  the  sympathetic  fibers,  which  sur- 
round the  cells  abundantly,  come  into  consideration.  It  must  not  be  overlooked,  how- 
ever, that  we  know  of  marked  changes  occurring  in  the  spinal  ganglia  in  tabes  (Vul- 
pian,  Wollenberg,  and  others)  which  have  been  unaccompanied  by  herpes  or  any- 
thing related  to  it. 

The  roots  enter  the  cord  in  longitudinal  rows. 

Where  large  roots,  corresponding  to  the  extremities,  enter  the  cord, 
the  latter  is  greater  in  size  than  elsewhere.  The  intumescentia  cervicalis 
receives  and  gives  off  the  arm-nerves;  the  intumescentia  lumbalis,  the  leg- 
nerves.  The  smallest  portion  of  the  cord  emits  the  intercostal  nerves.  The 
lowest,  conical  portion  of  the  cord  is  called  conus  terminalis;  from  it  arises, 
in  addition  to  the  nerves,  a  long,  thin  process,  the  filum  terminate.  The 
superior  boundary  is  the  beginning  decussation  of  the  pyramidal  fibers  (see 
below). 

In  examinations  of  patients  the  important  question  often  arises,  from  what 
level  of  the  cord  emerge  the  particular  spinal  roots  supplying  paralyzed  muscles  or 
anaesthetic  areas  of  the  skin.  It  has  been  sought  to  solve  this  question  by  experi- 
ments on  animals,  than  which  anatomy  itself  could  not  serve  the  purpose  better. 
With  man  it  has  been  repeatedly  sought  to  derive  more  knowledge  on  this  point 
from  cases  of  localized  lesions  of  the  cord  (contusions,  hemorrhages,  etc.).  Follow- 
ing is  a  list,  slightly  modified,  taken  from  a  compilation  of  all  accessible  reports  of 
cases  up  to  1890,  made  by  Starr.  Probably  experience  will  dictate  changes  here  and 
there. 


2  I  I 


Ml 


336 


ANATOMY    OF    THE    CENTRAL   NERVOUS    SYSTEM. 


LOCALIZATION  OF  FUNCTION  IN  THE  DIFFERENT   SEGMENTS 
OF  THE  SPINAL  CORD. 


MUSCLES. 


REFLEXES. 


SKIN-SENSATIOJJ. 


5th  Cervical. 


6th  Cervical. 


7th  Cervical. 


8th  Cervical. 


1st  Dorsal. 


I  Inspiration    by    sudden 

Trapezius.  j     pressure     under     the 

Scaleni  and    neck-mus-      edge  of  the  ribs. 

cles. 
Diaphragm. 

Diaphragm.  Dilatation  of  the  pupil 

Supra-  and    infra-  spi-      on    irritation    of     the 

natus.  neck  ( 4  to  7  cervical ) . 

Deltoid. 
Biceps  and    coraco-bra- 

chialis. 

Supinator  lougus. 
Rhomboid. 


2d  and  3d  Cer-  Sterno-mastoid . 
vical. 


4th  Cervical. 


Deltoid. 

Biceps    and   coraco-bra- 

chialis. 
Supinator    longus    and 

brevis. 
Pectoralis  major  (clavic- 

ular portion). 
Serratus  magnus. 
Rhomboid. 
Brachialis  anticus. 
Teres  minor. 

Biceps. 

Brachialis  anticus. 
Pectoralis  major  (clavic- 

ular portion). 
Serratus  magnus. 
Triceps. 
Extensors  of  hand  and 

fingers. 
Pronators. 

Long  head  of  triceps. 
Extensors  of  hand  and 

fingers. 

Flexors  of  the  hand. 
Pronators  of  the  hand. 
Pectoralis  major  (costal 

portion  )  . 
Subscapular. 
Latissinms  dorsi. 
Teres  major. 

Flexors  of  the  hand  and 

fingers. 
Small  hand-muscles. 

Extensor  pollicis. 
Small  hand-muscles. 
Thenar  and  hypothenar 
eminences. 


Neck  and  back  of  head. 


Neck. 

Upper  part  of  shoulder. 

Outer  side  of  arm. 


Scapular  reflex  (5cer-  Posterior  surface  of 
vical  to  1  dorsal).  j  shoulder  and  arm. 

Tendon-reflexes  of  the !  Outer  side  of  arm  and 
corresponding  muscles,  forearm. 


Reflexes  of  the  extensor 
tendons  of  the  arm 
and  forearm. 

Wrist  tendon-reflexes  ( 6 
to  8  cervical ) . 


Outer  side  of  forearm. 
Dorsum  of  hand. 
Distribution  of   the  ra- 
dial nerve. 


Blow   on  lower   end   of   Radial  territory  of  the 
radius  producing  clos-  j     hand, 
ure  of  the  fingers. 

Palmar    reflex    (7    cer- 
vical to  1  dorsal ) . 


Territory  of  the  me- 
dian. 


Pupillary  reflex. 


Ulnar  territory'. 


PERIPHERAL-XERYE    ROOTS,    SPIXAL    GANGLIA,    SPINAL   CORD.          337 


SEGMENTS. 

MUSCLES. 

REFLEXES. 

SKIN-SKNSATION. 

2d    to     12th 
Dorsal. 

Muscles  of  the  back  and 
abdomen. 
Erector  spinse. 

Epigastric  (  4  to  7  dorsal  ) 
Abdominal  (7  to  11  dor- 
sal). 

Skin  of  the  breast,  back, 
abdomen,   and    upper 
gluteal  region  . 

1st  Lumbar. 

Ilio-psoas. 
Sartorius. 
Abdominal. 

Cremaster  (1  to  3  lum- 
bar). 

Skin   of   external  geni- 
talia. 
Anterior  part  of  scrotum. 

2d  Lumbar. 

Ilio-psoas. 
Sartorius. 
Flexors    of     the     knee 
(Remak?). 
Quadriceps  femoris. 

Patellar     (2  to  4  lum- 
bar). 

Outer  side  of  hip. 

3d  Lumbar. 

Quadriceps  femoris. 
Internal  rotation  of  the 
femur. 
Adductors  of  thigh. 

Anterior    and    internal 
sides  of  hip. 

4th  Lumbar. 

Abductors  of  thigh. 
Adductors  of  thigh. 
Tibialis  anticus. 
Flexors    of     the    knee 
(Ferrier?). 

(  Gluteal  reflex  (4  to  5 
/      lumbar). 

Inner   side   of   hip  and 
leg  to  the  ankle. 
Inner  side  of  foot. 

5th  Lumbar. 

External  rotators  of  the 
femur. 
Flexors    of     the    knee 
(Ferrier?). 
Flexors  of  the  foot. 
Extensors  of  the  toes. 
Peronei. 

' 

Posterior  side    of    hip, 
thigh,  and  outer  side 
of  foot. 

1st    and    2d 
i'Sacral. 

Flexors  of  the  foot  and 
toes. 
Peronei. 
Small  foot-muscles. 

Plantar  reflex. 

Posterior  side  of  thigh, 
outer  side  of  leg  and 
foot. 

3d     to      5th 
Sacral 

Muscles  of  perineum. 

:  Tendo-Achillis      reflex, 
vesical  and  rectal. 

Skin   of   sacrum,    anus, 
perineum,  and  genita- 
lia. 

The  course  of  the  fibers  in  the  spinal  cord  is  but  partially  known.  To 
understand  it  one  must  familiarize  one's  self  with  the  cross-section  of  the 
cord.  In  such  a  section  one  finds  first  a  peripheral  white  substance  and  a 
central  H-shaped  gray  substance. 

The  two  halves  of  the  spinal  cord  are  divided  by  the  anterior  and  pos- 
terior longitudinal  fissures,  and  connected  by  a  commissure  of  white  sub- 
stance anteriorly,  of  gray  matter  posteriorly.  The  anterior  broad  portions 
of  gray  matter  are  called  the  anterior,  or  ventral,  horns,  and  the  posterior 
extension  of  gray  matter,  the  posterior,  or  dorsal,  horns. 

The  proportions  of  the  white  to  the  gray  substance  at  different  levels  of 


338 


ANATOMY    OF    THE    CENTRAL    NERVOUS    SYSTEM. 


the  cord  are  not  the  same.  Especially  does  the  gray  matter  predominate 
from  the  upper  lumbar  region  downward.  Fig.  217  gives  cross-sections  of 
different  levels  of  the  cord.  Beside  the  varying  proportions  of  gray  and 
white  matter,  one  sees  also,  that  the  lateral  portion  of  the  ventral  horn  in  the 
lower  cervical  and  upper  dorsal  cord  becomes  more  and  more  prominent  and 
finally  (Fig.  217,  Dt  and  D3)  becomes  distinct  as  the  lateral  horn,  or  tractus 
intermedio-lateralis.  In  the  lower  dorsal  cord  it  is  lost  again.  In  Fig.  216 
it  is  indicated  by  o. 

In  the  entire  cervical  and  upper  dorsal  cord,  the  gray  matter  between 
the  tractus  intermedio-lateralis  and  the  ventral  horn  is  not  sharply  denned, 


Fig.  216. — Half-schematic  transverse  section  of  the  spinal  cord,  a,  Ante- 
rior and  ft,  posterior  longitudinal  fissure,  c,  Anterior  column,  d,  Lateral  column. 
e,  Posterior  column,  f,  Funiculus  gracilis,  g,  Funiculus  cuneatus.  li,  Anterior, 
and  i,  Posterior  roots,  k,  Central  canal.  I,  Sulcus  intermedialis  posterior,  m, 
Anterior  horn,  n,  Posterior  horn,  o,  Tractus  intermedio-lateralis.  p,  Processus 
reticularis.  q,  Anterior  white  commissure,  r,  Posterior  gray  commissure,  s, 
Clarke's  column,  or  columna  vesicularis.  (After  Erb.) 


but  presents  a  net-work  of  gray  bands  and  fibers,  which  pushes  out  into  the 
white  substance.  It  is  called  processus  reticularis. 

In  the  conus  terminalis  the  gray  matter  is  inclosed  in  a  very  thin  layer 
of  white  fibers  (Co  in  Fig.  217). 

The  root-fibers  of  the  motor  nerves  pass  the  spinal  ganglia  and  enter 
the  cord,  penetrating  its  white  substance  to  join  the  ventral  horns.  All  of 
the  axis-cylinders  contained  in  them  join,  as  shown  in  Fig.  218,  each  with 


PERIPHERAL-NERVE    ROOTS,    SPINAL   GANGLIA,    SPINAL   CORD.          339 

one  of  the  large  ganglion-cells  of  the  horns.  A  cell  of  the  anterior  horn 
with  many  branches  is  shown  in  Fig.  4  and  in  Fig.  6,  D.  Not  all  these  cells 
are  in  direct  relationship  with  the  root-fibers. 

The  ventral-horn  cells  are  largely  arranged  in  groups.     The  exact  relationship 
between  these  groups  and  the  roots  is  but  partly  known.    Naturally  much  knowledge 


Fig.  217.— Sections  of  the  cord  at  different  levels.  The  letters  and  figures 
indicate  the  spinal  nerves,  the  exits  of  which  correspond  to  the  respective  sec- 
tions. (Quain.) 


\vould  be  gained  if  in  every  case  where  in  life  there  was  well-defined  peripheral  loss 
there  should  follow  after  death  a  careful  examination,  specially  directed  toward  the 
localization  of  altered  ganglion-cells.  Hence  it  will  be  helpful  to  become  acquainted 
with  the  cell-groups  in  the  spinal  gray  matter,  which,  being  confirmed  by  mor- 
phology, represent,  for  the  present,  all  that  is  actually  known.  We  are  indebted  to 
Waldeyer  for  a  classification  of  these  cells,  represented  in  Fig.  219.  The  well-d» 


340 


AXATOilY    OF    THE    CENTRAL    NERVOUS    SYSTEM. 


fined  groups  of  the  cervical  portion  and  those  of  the  lumbar  cord,  containing  espe- 
cially numerous  cells,  are  less  developed  in  the  dorsal  part  of  the  cord,  corresponding 
to  its  smaller  volume  and  perhaps  also  to  the  different  functions  of  the  nerves 
arising  from  it. 

None  of  these  groups,  excepting,  perhaps,  the  posterior  median  group,  can  be 
followed  continuously  throughout  the  cord.  There  is  much  to  indicate  that  this 
group  serves  to  innervate  the  muscles  of  the  back.  As  seen  in  the  tables  on  pages 
336  and  337,  the  brachial  plexus  arises  from  the  cervical  cord.  For  its  various 
elements  a  thorough  investigation  of  all  the  cases  in  which  loss  of  function  was 
present  as  a  symptom  of  spinal  disease  (Kayser,  Collins)  points  out  the  nuclei. 


-T 


Fig.  218. — From  the  anterior  border  of  a  cross-section  of  the  anterior  gray 
horn.  Transition  of  a  cell-process  into  the  anterior  root.  Carmine  preparation 
"%.  (After  Henle.) 


From  the  lateral  group  in  the  cervical  cord  come  the  flexor  nerves,  from  the  more 
median  group  those  for  the  extensors  of  the  arm  and  the  hand. 

The  roots  of  the  sensory  nerves  enter,  after  passing  through  the  spinal 
ganglia,  partly  direct  in  the  posterior  horn,  partly  in  the  posterior  white 
columns.  The  cells  of  the  spinal  ganglion  form  the  sources  of  the  majority 
of  these  fibers.  It  will  be  remembered  that,  as  embryology  teaches,  the  axis- 


PERIPHERAL-NERVE    ROOTS,    SPINAL.  GANGLIA,    SPJNAL    CORD.          341 

cylinders  from  the  cells  of  these  ganglia  extend  peripherally  in  the  sensory 
nerves,  and  centrally  into  the  cord. 

The  central  branches  form  what  we  call  the  posterior  roots.  With  them 
pass  other  fibers,  however,  which  do  not  arise  from  the  cells  in  the  spinal 
ganglion. 

A  case  observed  by  Leonowa  shows  how  independent  of  each  other  are  the 
dorsal  roots  and  the  spinal  cord  in  their  development.  The  entire  elementary  cord 
was  missing  in  a  monster,  but  the  spinal  ganglia  were  present,  and  from  them  arose 
peripheral  nerves,  besides  entire  bundles  of  posterior  roots,  which,  of  course,  ended 
free  in  the  vertebral  canal. 


The  ganglion-cells  of  the  dorsal  horns  are  smaller  than  those  of  the 
ventral  horns.  For  the  most  part  they  have  a  spindle-shaped  form.  Their 
axis-cylinders  divide  either  soon  after  quitting  the  cell-body  into  a  fine 
arborization  like  that  shown  in  Fig.  152,  g,  or  they  enter  farther  into  the 
substance  of  the  cord.  They  never  become  peripheral  nerve-fibers. 

Two  groups  are  readily  distinguished  by  the  naked  eye  in  the  posterior 
horns,  from  their  form  and  color.  The  group  called  columna  vesicularis, 
first  studied  by  Stilling,  afterward  more  exactly  by  Clarke,  generally  known 
as  Clarke's  column,  lies  about  where  the  ventral  and  dorsal  horns  come  to- 
gether (Fig.  216,  s).  Besides  the  cells,  it  contains  a  fine  net- work  of  fibers, 
and  bundles  of  especially  delicate  fibers  running  longitudinally.  On  cross- 
section  its  rounded  form  is  distinct,  and  can  be  followed  from  about  the 
end  of  the  cervical  enlargement  to  the  beginning  of  the  lumbar  enlarge- 
ment. Single  cells,  however,  in  appearance  similar  to  Clarke's  cells,  are  met 
with  higher  up  even  to  the  medulla  oblongata. 

Still  more  sharply  defined  than  the  Stilling-Clarke  column  appears  the 
siibstanUa  gelatinosa  Rolandi,  in  the  gray  matter  of  the  posterior  horn.  It 
lies  near  the  point  of  the  horn,  and  is  perforated  by  numerous  afferent  fibers 
from  the  posterior  root.  Until  our  staining-methods  were  sufficiently  de- 
veloped, the  importance  of  this  peculiar,  glass-like,  translucent  substance 
remained  in  doubt.  Only  in  the  last  few  years  has  it  been  discovered  that  it 
contains  cells  of  similar  character  to  those  lying  in  the  posterior  horns. 

What  became  of  their  axis-cylinders  seemed  especially  difficult  to  determine 
in  a  region  so  densely  filled  with  axis-cylinders  and  collaterals.  Recently,  however, 
S.  Eam6n  y  Cajal  and  particularly  v.  Lenhossek  were  able  to  show  that  the  axis- 
cylinders  of  the  spindle-shaped  cells  (marginal  cells  in  Fig.  219),  passing  around  the 
periphery  of  the  Rolandic  substance,  arrive  at  the  dorsal  portion  of  the  lateral  col- 
umn, and  that  those  of  the  narrower,  stellate  cells  of  the  Rolandic  substance  itself 
enter  the  neighboring  posterior  column  and  the  so-called  marginal  zone  of  the  poste- 
rior horn.  The  latter  cells  possess  not  only  one,  but  several  processes  of  the  his- 
tological  character  of  an  axis-cylinder. 


342 


ANATOMY    OF   THE    CENTEAL   NEKVOUS    SYSTEM. 


The  white  matter,  surrounding  the  gray,  consists  principally  of  longi- 
tudinally directed  fibers,  together  with  the  oblique,  ascending  fibers  of  the 
nerve-roots  and  certain  other  fibers,  which  pass  out  at  more  or  less  of  a  right 
angle  from  the  gray  matter  to  the  white  columns.  The  nerve-fibers  have 
an  axis-cylinder  and  a  medullary  sheath.  The  thickness  of  this  sheath  varies 
greatly.  They  do  not  possess  a  sheath  of  Schwann. 

The  axis-cylinder  presents  a  fibrillated  appearance,  wherever  examined. 
Probably  it  is  made  up  of  numerous  fibrils.  Eecent  investigations  have 
shown  that  the  axis-cylinders  of  the  nerve-fibers  in  the  spinal  cord,  at  their 
extremities,  do  not  end  as  a  whole,  but  by  a  kind  of  splitting.  With  all 
the  long  nerve-fibers  in  the  white  matter  and  also  in  the  gray  matter,  one 


ffinterhortt 
Zellend  Sut>st  Rolando 
Marytnatf  Jt.-homzeUen 
Centrate  ff.  -fo>rn.ze& 


Fig.  219.—  (After  Waldeyer,  slightly  modified.) 
Sections  through 


Inferior  portion  of  cervical  enlargement. 


Lumbar  enlargement. 


The  divisions  are  made  according  to  the  structures  brought  out  by  stain- 
ing an  adult  cord  with  carmine.  Other  methods  show  that,  at  least  in  the 
fetal  cord,  in  certain  regions  there  are  a  great  many  more  individual  cells 
than  are  here  represented.  Hintcrhorn,  Posterior  horn.  Zellen  <i.  Sub.  Rol., 
Cells  of  the  subst.  Rolando.  Marginale  H.-hornzellen,  Marginal  cells  of  post. 
horn.  Centrale  H.-hornzellen,  Central  cells  of  post.  horn.  Basale  H.-hornzellen, 
Basal  cells  of  post.  horn.  Stilling-Clarke  Zell,  Stilling-Clarke's  cells.  Mittel- 
zellen,  Middle  cells.  Lot.  hint.  Gruppe,  Lateral  posterior  group.  Laterale  vord. 
Gr.,  Lateral  anterior  group.  Mediate  hint.  Gruppe,  Median  posterior  group. 
Mediale  rord.  Gruppe,  Median  anterior  group.  Former/torn,  Anterior  horn. 

finds  at  certain  points  that  a  delicate  fibril  separates  off  at  right  angles  to 
the  axis,  passes  toward  the  gray  matter,  and  there,  as  has  been  observed,  it 


PERIPHERAL-XERVE    ROOTS,    SPINAL   GANGLIA,    SPINAL    CORD.          343 


ends  in  a  minute  brush.    The  places  from  which  pass  off  these  "collaterals" 
from  the  stem  are  usually  marked  by  a  slight  enlargement. 

The  spinal  white  matter  is  interwoven  with  numerous,  radiating  septa, 
made  up  of  neuroglia,  and  in  them  run  the  blood-vessels,  coming  from  the 
periphery  of  the  cord. 

The  nerve-fibers  in  the  white  matter  are  all  surrounded  by  a  loose  net-work  of 
In  the  gray  matter  it  is  found  most  densely  deposited  near  the 


Fig.  220. — Longitudinal  section  through  the  lateral  column  of  a  newborn 
pup.  On  the  left  is  shown,  after  an  original  preparation  of  Ramon  y  Cajal's,  axis- 
cylinders  sending  collaterals  into  the  gray  matter,  and  others,  coming  from  cells 
there  situated,  dividing  into  an  ascending  and  a  descending  branch.  The  cellular 
connections  to  the  right  are  schematic. 


central  canal,  in  the  substantia  grisea.  After  the  Weigert  stain,  it  appears  to  the 
naked  eye  as  a  dark-blue  spot. 

Less  dense  than  this,  but  thicker  than  in  the  white  matter,  is  the  neuroglia- 
mesh  of  the  ventral  horns.  It  is  most  sparse  in  the  substantia  gelatinosa  Rolandi. 

The  entire  periphery  of  the  cord  is  covered  with  a  thin  mantle  of  almost  pure 


344  ANATOMY    OF    THE    CENTRAL   NERVOUS    SYSTEM. 

neuroglia:  the  peripheral  gelatinous  layer  (Fig.  219,  to  the  right).  Also  on  the  point 
of  the  dorsal  horns  there  is  found  an  especially-thick  development  of  glia.  Here 
the  entering  posterior  roots  suffer,  mostly  at  the  expense  of  their  medullary  sheaths, 
and  appear  very  compact,  as  if  tied  together,  in  a  section.  (Obersteiner  and  Eedlich.) 
Fig.  5  explains  the  epithelium  of  the  central  canal  in  the  fetus.  In  youth, 
also,  the  cells  lie  in  regular  rows  on  the  layer  of  neuroglia.  They  lose  their  cilia 
probably  soon  after  birth,  although  during  life  there  remains  a  peculiar  layer  of 
small,  evenly  placed  nodules  on  the  central  edge  of  the  cells,  which,  during  the 
fetal  period,  are  found  just  at  the  bases  of  the  cilia.  With  increasing  age,  the 
resistance  of  the  epithelial  cells  lessens.  They  become  separated  from  each  other, 
neuroglia-fibers  appear  between  them,  they  even  loosen  from  their  bases,  and  lie  in 
apparent  confusion  or  in  small  groups  between  and  among  the  developing  neuroglia- 
tissue.  As  a  result,  there  is  in  the  place  of  the  original  central  canal  a  mass  of  cells 
leaving  either  no  lumen  at  all  or  perhaps  several  small  lumina  in  the  center  of  the 
cord. 

This  much  has  been  ascertained  by  the  examination  of  sections  of  the 
adult  cord.  But  in  a  knowledge  of  the  minute  structure  of  the  cord,  much 
more  has  been  learned. 

As  one  sees  in  the  cross-section  of  the  cord,  it  is  divided  into  columns 
by  the  spinal  nerve-roots  and  by  the  longitudinal  fissures.  Median  to  the 
roots  lie  the  anterior  and  posterior  columns;  lateral  to  them,  the  lateral 
columns. 

The  study  of  embryology,  as  well  as  that  of  the  effects  of  interruption 
of  the  fibers,  and  the  examination  of  certain  diseases  of  the  spinal  cord  have 
taught  that  these  anterior,  posterior,  and  lateral  columns  are  not  homogene- 
ous, equivalent  bundles  of  fibers,  as  might  appear  on  casual  inspection  of  a 
cross-section  of  a  healthy,  adult  cord,  but  that  they  are  composed  rather  of 
several  divisions. 

It  will  be  remembered  that  the  tractus  cortico-spinalis,  the  pyramid, 
passes  from  the  cortex  of  the  motor  region  down  through  the  internal  cap- 
sule and  the  pes  cerebri  to  the  ventral  portion  of  the  pons.  Where  does  it 
pass  in  the  medulla  spinalis?  It  is  not  difficult  to  find.  When  anywhere  in 
its  long  course  it  is  destroyed  by  a  disease-focus,  its  fibers  gradually  dis- 
appear, being  displaced  by  connective  tissue.  This  degeneration,  called 
secondary  degeneration,  proceeds  downward  into  the  cord.  It  takes  place 
there  in  two  locations:  one  in  the  median  portion  of  the  anterior  column  of 
the  same  side  as  the  cerebral  lesion,  and  the  other  in  a  large  portion  of  the 
lateral  column  of  the  opposite  side.  Higher  up,  at  the  beginning  of  the  bulb, 
one  sees  that  this  crossed  tract  passes  over  to  the  direct  tract,  decussating 
with  the  sound  fibers  of  the  opposite  side. 

The  tract,  which  is  affected  by  the  degeneration,  is  called  in  the  cord, 
as  in  the  brain,  the  tractus  cortico-spinalis,  or  the  pyramidal  tract.  In  the 
cord  it  divides  into  the  pyramid  of  the  anterior  column  (median  part  of  the 
column)  and  the  pyramid  of  the  lateral  column  (in  its  posterior  half).  There 


PERIPHERAL-NERVE    ROOTS,    SPINAL    GANGLIA,    SPINAL   CORD.          345 

is  ground  for  the  assumption  that  these  pyramidal  tracts  contain  the 
majority  of  the  fibers  extending  from  the  brain  to  the  cord,  which  subtend 
acquired  movement.  They  degenerate  only  downward;  their  fibers  dis- 
appear regularly,  if  the  tract  be  destroyed  anywhere  in  the  brain  or  the  cord. 
In  the  area  of  the  lateral  columns,  occupied  partly  by  the  tractus  cortico- 
spinalis,  there  are  to  be  found  other  fibers,  which,  belonging  to  the  associa- 
tion-bundles of  the  cord,  join  its  different  levels  together.  The  longest  fibers 


Fig.  221. —Scheme  of  the  descending  degeneration  in  the  tractus  cortico-spinalia 
in  a  case  of  focal  lesion  in  the  left  internal  capsule. 


of  this  category  are  in  this  territory.  So  it  happens,  in  case  of  lesion  of  the 
lateral  column  of  the  cord,  that  a  larger  area  degenerates  downward  than 
accords  with  the  spread  of  the  pyramids  in  the  medulla  oblongata.  From 
this  circumstance  has  arisen  the  common  error  of  supposing  that  the  pyra- 
mids receive  fibers  from  the  cord  itself. 

At  birth  all  the  tracts  of  the  cord,  in  man,  have  received  their  medul- 
lary sheaths.     Only  the  tractus  cortico-s pinoles  form  exceptions.    "With  the 


346 


ANATOMY   OF   THE    CENTRAL    NERVOUS    SYSTEM. 


newborn,  therefore,  in  a  cross-section  of  the  cord  the  pyramidal  tracts  appear 
gray  among  the  white  fibers  surrounding. 

With  the  lower  animals,  corresponding  to  the  more  meagre  expansion  of  the 
cerebral  cortex,  the  pyramidal  tracts  are  rela- 
tively smaller  than  in  man.  Even  here  they 
contain  probably  only  fibers  for  those  muscles, 
which  principally  are  used  by  the  co-operation 
of  the  cortex, — hence,  in  such  actions  as  are 
deliberate  and  acquired.  At  any  rate,  after 
the  separation  of  those  of  their  fibers  which 
supply  the  upper  extremities  they  are  ma- 
terially reduced  in  size,  remain  approximately 
equal  throughout  the  dorsal  cord,  and  after 
losing  the  fibers  for  the  lower  extremities  they 
are  so  reduced  in  volume  that  they  ai-e  prac- 
tically wanting  in  the  lower  lumbar  cord. 
Examinations  of  these  tracts  in  animals  that 
make  greater  use  of  the  Rands — apes,  burrow- 
ers — and  in  those  that  use  the  hind-extremities 
the  more — as  some  marsupials — were  desirable. 
But  they  would  have  to  be  based  on  embryo- 
logical  or  degenerative  data,  as  only  in  such 
wise  can  the  pyramidal  tracts  be  differen- 
tiated. 

The  examination  of  secondarily  de- 
generated spinal  cords  enables  us  to  know 
still  more  of  the  combinations  of  the 
white  columns.  In  a  cord  that  has  been 
destroyed  in  the  dorsal  region  by  pressure 
or  some  other  lesion  one  finds,  as  the 
foregoing  leads  one  to  expect,  below  the 
place  of  lesion  the  corresponding  pyra- 
mid degenerated.  But  there  appears  also 
a  degeneration  in  the  other  direction. 
It  includes,  near  the  lesion,  the  entire 
area  of  the  posterior  columns;  but,  a  few 
segments  higher,  is  confined  to  the  me- 
dian portion  of  these  columns,  that  part 
next  the  median  fissure.  In  such  sec- 
tions we  can  easily  distinguish,  in  the 
posterior  columns,  an  external  and  an 
internal  tract.  That  which  degenerates 
upward  in  these  columns  (as  far  as 
the  medulla  oblongata)  is  fibers  com- 
ing from  the  dorsal  roots,  and  cut 


Fig.  22. — Secondary  descending  de- 
generation after  lesion  in  the  left 
cerebral  hemisphere.  (After  Erb.) 


PERIPHERAL-NERVE    ROOTS,    SPIXAL    GANGLIA,    SPINAL   CORD.          347 

off  from  their  ganglion-cells  in  the  spinal  ganglia.  If  one  experimentally 
divides  these  roots  next  to  the  cord,  one  produces  exactly  the  same  area  of 
degeneration.  Just  above  the  place  of  division  both  the  external  and  the 
internal  posterior  columns  are  degenerated;  but  farther  up,  where  new, 
healthy  root-fibers  have  entered,  the  latter  lie  external  to  those  degenerated, 
-and,  as  one  ascends,  these  affected  fibers  approach  ever  nearer  the  median 
line. 

What  we  have  just  learned  by  an  examination  of  the  degenerated  pos- 
terior columns  is  reinforced  by  studying  the  development  of  the  medullary 
sheaths.  It  teaches,  too,  that  there  are  at  least  two  fiber-systems  there:  one 
external,  usually  known  as  the  prime  biindle  of  the  posterior  columns;  also 


Fig.  223. — Transverse  section  through  the  cervical  cord  of  a  newborn  child. 
The  pyramidal  tracts,  minus  medullated  fibers,  appear  translucent  and  clear. 
The  direct  pyramidal  tract  extends  far  over  into  the  antero-lateral  column. 
Wwrzel-Zvne,  Root-zone.  KleinJiirnseitenstranfl-Bahn,  Lateral  cerebellar  tract. 
Grenzscliicht,  Boundary  layer  or  zone.  Seitenstrang,  Lateral  column.  YonJir- 
straiuj.  Anterior  column.  GriDidliiindcl,  Ground-bundle. 


called  the  funiculus  cuneatus,  or  column  of  Burdach;  and  one  internal, 
called  the  funiculus  gracilis,  or  column  of  Goll.  In  the  normal  cord  of  the 
adult  these  two  s}rstems  are  separated  from  each  other  by  a  connective-tissue 
septum  only  in  the  cervical  portion,  while  in  the  lower  sections  they  can  only 
then  be  distinguished  when  one  or  the  other  is  diseased,  when  they  differ 
in  color.  The  columns  of  Goll  increase  in  volume  from  below  upward,  as  far 
as  the  lower  dorsal  cord,  because  they  conduct  portions  of  the  continuously- 


348  ANATOMY   OF    THE    CENTRAL   NERVOUS    SYSTEM. 

entering  posterior  roots  from  the  sensory  nerves  of  the  legs  to  the  medulla 
oblongata. 

Later  it  will  be  seen  that  still  other  subdivisions  must  be  made  in  the 
posterior  columns. 

The  manner  of  propagation  of  diseases  in  them,  particularly  the  results 
of  submitting  fresh  lesions  of  the  cord  to  the  Marchi  process  of  staining, 
which  places  the  single  degenerated  medullary  sheaths  under  the  action  of 
a  special  reagent,  has  largely  added  to  our  knowledge  of  these  tracts. 

That  portion  which  closely  adjoins  the  gray  commissure  (A  in  Fig.  223) 
must  contain  a  separate  system  of  fibers,  because,  in  tabes  for  example,  it 


Fig.  224. — Secondary  degenerations,  ascending  and  descending,  after  a  transverse 
lesion  of  the  upper  dorsal  cord.      (After  Striimpell. ) 

never  participates  in  the  disease,  even  when  the  remainder  of  the  posterior 
columns  degenerates.  It  may  be  termed  the  ventral  field  of  the  posterior 
columns. 

The  posterior  columns  consist  almost  exclusively  of  fibers  entering  by 
way  of  the  'posterior  roots.  These  roots  are  so  arranged  that  the  entering 
fibers  lie  always  laterally,  close  up  to  the  posterior  horns,  but  that  those 
entering  later,  therefore  higher  in  the  cord,  shove  the  more  early  arrived 
fibers  toward  the  median  line.  So  it  happens  that  in  the  cervical  part  of 
the  cord  the  fibers  from  the  lower  extremities  occupy  principally  Goll's 
column,  while  the  column  of  Burdach  still  contains  many  fibers  from  the 


PERIPHEKAL-XERYE    ROOTS,    SPINAL   GANGLIA,    SPINAL    CORD.          349 

upper  extremities.  It  must  not  be  suspected  that  the  portions  of  the  pos- 
terior columns  named  contain  all  the  fibers  of  a  posterior  root.  Many  fibers, 
immediately  after  entering  the  cord,  gain  the  gray  matter,  while  others 
bend  in  their  course,  to  pass  through  the  posterior  columns.  Therefore 
there  lie  in  the  upper  sections  of  the  cord  relatively  few  of  those  fibers  in 
the  posterior  columns  which  entered  lower  down.  Experimentally  this  has 
been  proved  by  following  up  the  cord  from  a  divided  dorsal  root,  when  the 
degenerating  portion  of  the  cord  grows  smaller  and  smaller  as  one  ascends. 
At  the  same  time  the  degenerated  field  approaches  more  nearly  the  median 
line. 

In  the  highest  part  of  the  cord  the  funiculus  cuneatus  contains  fibers 
which  do  not  come  direct  from  the  dorsal  roots.  Their  origin  is  uncertain. 

A  part  of  the  posterior-root  fibers  extends  to  the  vicinity  of  Clarke's 
column  of  cells  and  there  arborizes  (Fig.  227).  From  this  column  of  cells 


Fig.  225. 


Fig.  226. 


Section  through  the  cervical  and  lumbar  cord,  with  approximately-drawn 
boundaries  of  the  different  divisions  of  the  white  matter.  Arranged  from  em- 
bryological  principles,  mainly  from  preparations  with  secondary  degenera- 
tion of  one  or  more  of  the  tracts.  Iff,  Crossed  pyramidal  tract.  1,  Direct  py- 
ramidal tract.  2,  Antero-lateral  ground-bundle.  3,  Tractus  cerebello-spinalis 
ventralis.  4,  Tractus  cerebello-spinalis  dorsalis.  5,  Lateral  marginal  zone.  6, 
Postero-lateral,  or  Burdach's,  column.  7.  Postero-median,  or  Coil's,  column. 
8,  Radicular  zone.  9,  Ventral  field  of  the  posterior  column. 


arises  another  tract  of  fibers.  After  section  of  the  cord  this  tract  degenerates 
upward.  It  is  the  peripheral  portion  of  the  lateral  column  (4  in  Fig.  225). 
This  tract  may  be  followed  to  its  entrance  in  the  vermis  of  the  cerebellum, 
and  is  called  the  tractus  cerebello-spinalis  dorsalis.  We  are  particularly  in- 
debted to  embryological  research  (Flechsig)  for  our  knowledge  of  this,  the 
direct  cerebellar  tract,  and  for  our  ability  to  distinguish  it  from  the  other 
lateral  tracts.  In  the  first  few  weeks  post-partum,  when  the  pyramidal  tract 


350  ANATOMY    OF   THE    CEXTEAL   NERVOUS    SYSTEM. 

still  lacks  its  medullary  sheath,  the  direct  cerebellar  tract  forms  a  delicate- 
white  border  along  the  periphery  of  a  large  part  of  the  lateral  column 
(Fig.  223). 

Later  investigations  (Loewenthal,  Mott)  have  shown  that  the  ventral 
portion  of  the  lateral  cerebellar  tract,  which  Gowers,  from  pathological  find- 
ings, had  already  distinguished  as  the  antero-lateral  tract,  does  not  arise 
from  Clarke's  cells,  but  from  other  cells  in  the  gray  matter.  This  tractus 
cerebello-spinalis  ventralis  courses  along  with  the  corresponding  dorsal  tract 
up  to  the  bulb,  but  is  separated  from  it  there,  and,  extending  farther  for- 
ward, enters  the  vermis  superior  of  the  cerebellum  with  the  peduncles  (vide 
page  328). 

Up  to  this  point  then,  from  the  study  of  secondary  degenerations  and 
embryology  we  have  learned  to  recognize  in  the  white  matter  the  following 
divisions  (systems  of  fibers,  so-called):  In  the  anterior  columns  the  direct 
pyramidal  tract;  in  the  lateral  columns,  the  crossed  pyramidal  and  direct 
cerebellar  tracts;  in  the  posterior  columns,  the  tracts  of  Burdach  and  Goll. 

In  Figs.  225  and  226  are  represented  all  of  the  white  tracts  mentioned. 
The  tract,  marked  2,  reaching  from  the  anterior  column  around  to  the  lateral 
column,  has  not  been  described.  This  area,  pierced  by  the  ventral  roots,  is 
known  as  the  anterior  radicular  zone.  That  pottion  of  it  lying  within  the 
anterior  column  is  also  called  the  anterior  ground-bundle.  The  portion  lying 
within  the  lateral  column  is  correspondingly  further  known  as  the  antero- 
lateral  mixed  zone. 

Further  divisions  in  this  region  should  doubtless  be  made;  but  as  yet 
the  recorded  cases  of  secondary  degeneration  do  not  enable  one  to  define  them 
exactly.  They  would  be  very  desirable,  since  it  is  to  the  anterior  column 
that  one  can  trace  the  fasciculus  longiludinalis  posterior,  and  it  was  into 
the  antero-lateral  mixed  zone  in  the  cat  that  Boyce  followed  that  tract  from 
the  "deep  gray"  of  the  optic  lobes  (ant.  corp.  quad.),  which  corresponds  to 
the  lateral  longitudinal  bundle  in  the  lower  vertebrates.  In  this  region  also 
are  to  be  found  the  prolongations  of  the  large  fibers  from  Deiter's  nucleus 
in  the  cerebellum,  shown  in  the  diagram,  Fig.  211,  after  Ferrier  and  Turner. 

Most  of  the  fibers  in  the  antero-lateral  column,  which  do  not  belong 
to  the  ventral  roots,  arise  in  the  gray  matter;  here  are  found,  besides,  in  all 
probability,  the  central  continuations  of  the  sensory  paths.  The  region  5 
(lateral  marginal  zone)  contains  fibers  coming  direct  from  the  posterior  roots, 
which,  after  crossing  through  the  dorsal  horn,  ascend  in  this  region  (Cf. 
Fig.  223,  right). 


CHAPTER    XXII. 
THE  COURSE  OF  THE  FIBERS  IN  THE  SPINAL  CORD. 

WHAT  becomes  of  these  fibers  after  their  entrance  through  the  spinal 
nerve-roots  into  the  cord?  How  much  farther  have  they  been  traced?  It  is 
not  the  form  or  shape  of  the  particular  part  of  the  central  nervous  system, 
but  rather  the  relationship  between  the  different  parts,  and  the  communica- 
tion between  fiber  and  fiber,  cell  and  cell,  that  must  be  the  basis  of  in- 
vestigations. 

The  anterior  root-fibers  may  be  traced  backward  and  slightly  upward, 
as  they  pass  through  the  anterior  radicular  zone.  Each  single  root  seems 
spread  out  over  a  large  extent  of  the  cord.  Arrived  at  the  border  of  the 
gray  matter,  the  component  fibers  separate.  As  to  what  occurs  to  them 
further,  there  are  many  and  varied  opinions.  The  following  statement, 
based  largely  on  personal  investigation,  includes  the  most  important  of  these. 

And  first  it  is  to  be  accepted  as  settled  that  certain  fibers  of  the  anterior 
root  arrive  at  the  ventral  horn-cells,  or  rather  form  their  axis-cylinder  proc- 
esses (see  Fig.  218).  Some  of  them  pass  over  to  cells  in  the  opposite  anterior 
horn,  by  way  of  the  anterior  commissure. 

On  pathologic  grounds,  it  has  long  been  recognized  that,  to  the  cell- 
centers  of  the  motor-nerves,  fibers  pass  from  the  cerebral  cortex  through 
the  cortico-spinal  tracts.  It  is  not  difficult  to  understand  that  numerous 
fibrils  from  the  area  of  the  anterior  pyramidal  tract  (direct  pyramidal  tract), 
crossing  over  through  the  anterior  commissure,  enter  the  opposite  anterior 
horn.  Most  of  these  fibrils  are  collaterals  from  the  fibers  proper  of  this 
pyramidal  tract.  In  the  anterior  horn  they  divide  up  into  fine  tufts,  which 
arborize  around  the  ganglion-cells.  Only  in  the  recent  past  has  the  assump- 
tion of  a  connection  between  these  cells  and  the  lateral  or  crossed  pyramidal 
tracts  been  proved.  Here  again  it  is  mainly  a  matter  of  collaterals  which 
are  given  off  from  these  tracts  and  enter  directly  the  ventral  horn  of  the  same 
side,  and  there  form  a  fine  arborization. 

The  pyramidal  tracts,  therefore,  are  the  secondary  motor  tracts. 
Through  the  close  contact  of  their  axis-cylinders  they  enter  into  relationship 
with  the  cells  of  origin  of  the  primary  motor  tract.  In  Fig.  7  this  is 
schematically  represented. 

(351) 


352  ANATOMY   OF   THE    CENRTAL   NERVOUS    SYSTEM. 

In  the  adult  cord  these  relations  are  not  discoverable.  One  must  make  use  t>f 
embryonic  cords,  in  which  the  pyramidal  fibers  are  as  yet  non-medullated,  then  stain 
with  silver  after  Golgi's  rapid  method,  and  prepare  longitudinal  and  diagonal  sec- 
tions. In  such  sections  one  may  often  trace  the  collaterals,  given  off  at  right  angles 
from  the  pyramidal  fibers  and  entering  the  gray  matter  ( cf.  Fig.  227 ) .  These  branches 
must  later  be  medullated;  for,  in  cases  of  degeneration  of  the  pyramids,  one  finds 
invariably  the  corresponding  ventral  horn  poorer  in  medullated  fibers  than  normally 
(Fiirstner).  The  same  branches  show  very  distinctly,  when  one  succeeds  in  staining 
them  with  osmium  during  their  degeneration  (Fig.  228,  sec.  5). 

Many  difficulties  oppose  themselves  to  the  study  of  the  relations  of  the 
posterior  nerve-roots.  Their  fibers  all,  or  nearly  all,  divide,  immediately 
after  entering  the  cord,  into  an  ascending  and  a  descending  branch.  From 
these  arise  numerous  collaterals  that  pass  partly  to  the  gray  matter,  partly 
into  the  posterior  columns  (vide  Fig.  227). 

The  fate  of  single  divisions  of  the  roots  is  very  varied;  their  relations 
are  extremely  complicated,  so  far  as  is  now  known.  In  view  of  this,  it  will  be 
well  to  refer  frequently  to  Fig.  227  while  considering  what  follows.  This 
figure  represents  what  is  actually  known.  It  implies  that  which  concerns 
the  multitude  of  fibers,  and  not  any  single  section.  Its  purpose  is  merely 
to  elucidate  the  text. 

In  a  cross-section  of  the  spinal  cord  one  recognizes  that  the  posterior 
roots,  at  their  entrance,  are  definable  into  at  least  five  parts.  The  most 
median  bundles  (1),  mainly  consisting  of  large  fibers,  nearly  all  enter  the 
posterior  columns  immediately  (posterior  root-zone).  Here,  as  we  have 
learned,  they  turn  upward  toward  the  brain.  The  behavior  of  these  roots, 
upon  secondary  degeneration  following  their  section,  teaches  that  those 
bundles  which  enter  directly  into  the  dorsal  column  are  afterward  pushed 
toward  the  median  line  by  those  entering  at  a  higher  level,  so  that  the 
caudal  root-fibers  occupy  above  a  position  near  the  middle  line,  in  Goll's 
column,  and  Burdach's  column  is  largely  made  up  of  such  fibers  just  enter- 
ing and  ascending  diagonally  (Fig.  28).  We  have  also  learned  that,  while 
running  thus  diagonally,  there  are  fibrils  continually  being  given  off,  which 
enter  the  gray  matter. 

Immediately  after  entering  the  cord,  before  the  fiber  turns  cephalad,  a 
branch  is  given  off  which  turns  caudad.  Its  course  is  now  better  known, 
since  examinations  of  fresh  secondary  degenerations  were  made  by  the 
Marchi  method  (Schaffer,  Lowenthal,  and  others). 

In  general,  the  traces  of  secondary  degeneration  on  examination  by 
this  method  appear  so  much  more  complicated  than  as  represented  in  the 
preceding  chapter  that  it  will  be  well  to  examine  the  accompanying  figures 
from  cases  described  by  Hoche  (Fig.  228). 

The  place  of  compression  lies  in  the  region  of  the  seventh  dorsal  vertebra.  The 
degeneration  at  that  point  (3),  as  indicated  by  the  osmium-blackened  points,  is 


THE    COURSE    OF    THE    FIBERS    IX    THE    SPINAL   CORD. 


353 


irregularly  spotted.  Behind,  toward  the  lumbar  region,  the  pyramids  separate  into 
their  anterior  and  lateral  tracts.  In  the  latter  there  degenerate  also  many  bundles 
of  greater  or  less  length,  which  belong  to  the  association-systems  connecting  different 
levels  of  the  cord.  Usually  the  shorter  fibers  lie  nearer  the  gray  matter,  while  the 
longer  ones  are  farther  away.  Naturally  these  association-tracts  are  degenerated 
most  of  all  at  points  immediately  above  and  below  the  place  of  compression; 
farther  away  in  either  direction  one  finds  only  a  few,  and  those  are  the  longest. 
In  the  posterior  columns  just  lateral  to  Goll's  column  there  pass  downward  for  a 


£/;  SettensiKB.)  V^f5^  \ 


Fig.  227. — Schema  of  cross-section  of  spinal  cord,  in  which  the  central  course 
of  some  important  bundles  is  indicated.  Compare  with  it  the  non-schematic  Fig. 
223,  right.  The  axis-cylinders  from  the  ventral  horn-cells  to  the  posterior  root 
are  omitted.  Tracts  of  the  first  order  shown  by  dark  lines,  those  of  the  second 
order,  by  dotted  lines.  For  translation  of  German  terms  see  explanation  accom- 
panying Fig.  223. 


distance  the  descending  fibers  from  those  root-bundles  which  are  affected  by  the 
compression.  They  form  a  comma-shaped  tract, — Schultze's  comma, — which  lies  in 
not  always  the  same  position,  according  to  the  particular,  interrupted  root.  This 
tract,  whose  relationship  to  the  dorsal  roots  is  still  disputed,  was  traced  by  Hoche  a 
distance  of  more  than  eight  vertebras  before  it  disappeared  in  the  gray  matter. 

Still  another  small  deposit  of  fibers,  lying  on  the  dorsal  side  of  the  posterior 

23 


354 


ANATOMY    OF    THE    CENTRAL    NERVOUS    SYSTEM. 


columns,  belongs  to  the  tracts  of  descending  degeneration.  In  the  lumbar  cord  it 
turns  in  toward  the  median  septum,  and  lies  close  to  it,  as  the  "oval  field"  (Flechsig). 
It  can  be  traced  into  the  conus  terminalis.  And,  while  its  termination  is  well 
known,  its  beginning  is  not,  it  having  been  traced  upward  only  to  the  cervical  region. 
For  the  present  it  will  be  well  to  designate  this  long  tract  of  very  thick  fibers  as  the 
dorsal  cervico-lumbar  tract. 


Medulla  cervicalis. 


Medulla  lumbalis. 

Fig.  228. — Compression  of  the  cord  at  the  level  of  the  seventh  dorsal  nerve. 
Ascending  degeneration  to  the  left,  descending  in  the  sections  on  the  right.  The 
products  of  degeneration  stained  black  with  perosmic  acid:  Marchi's  method. 
(After  Hoche.) 


A  second  portion  (2,  Fig.  227)  of  the  posterior  root-fibers  does  not  turn 
into  the  columns,  but  penetrates  the  white  matter  by  curves,  to  lose  itself 
in  Clarke's  column,  where  its  fibers  arborize  around  the  cells  of  that  column. 
Some  of  the  fibers  (3)  pass  directly  across  the  posterior  horn,  ventral  to 
the  substantia  gelatinosa  Eolandi,  and  then  course  farther  in  the  marginal 
zone  of  the  lateral  column.  They  are  well  shown  in  Fig.  223. 


THE    COURSE    OF    THE    FIBERS    IN    THE    SPINAL    CORD.  355 

The  portions  of  the  dorsal  roots  just  described  lie  to  the  median  side 
of  the  point  of  the  posterior  horn.  Lateral  to  it  (4)  lie  small  bundles  of 
coarse  fibers,  which  may  be  traced  through  the  substantia  gelatinosa,  and  the 
rest  of  the  horn  anterior  to  it,  up  to  the  large  cells  of  the  anterior  horn, 
around  which  they  arborize.  This  tract  is  usually  regarded  as  the  shortest 
reflex  path  (Fig.  33). 

More  laterally  still  (5)  are  root-fibers  which  enter  the  gray  matter  after 
a  longer  or  shorter  course.  These  fibers  split,  just  on  entering  the  periphery 
of  the  gray  matter,  or  soon  afterward  into  an  ascending  and  a  descending 
branch.  Many  of  them,  especially  large-fibered,  cross  through  the  sub- 
stantia gelatinosa  Rolandi  before  splitting.  From  these  two  divisions  there 
pass  out  numerous  collaterals  in  the  gray  matter,  especially  of  the  posterior 
horn,  where  they  subdivide  into  small,  thin  tufts,  around  the  cells  there 
found.  The  more  delicate  fibers  divide  generally  at  the  periphery  of  the 
posterior  horn.  So  there  arises,  between  the  point,  or  extremity,  of  the  pos- 
terior horn  and  the  periphery  of  the  cord,  a  field  which  is  filled  with  these 
ascending  and  descending  thin  fibrils  (zona  marginalis;  z.  terminalis) . 
From  this  zone  pass  continually  fine  fibrils  into  a  net-work  lying  between  it 
and  the  gelatinous  substance, — zona  spongiosa, — and  from  this  net-work 
arise  again  other  fine  fibers,  which  pass  through  the  substantia  gelatinosa, 
and  reach  the  fibrous  tangle  of  the  posterior  horn.  Probably  they  then  enter 
into  similar  relationship  to  the  cells  there,  as  the  coarse  fibers,  just  described. 

It  must,  however,  not  be  overlooked,  that  much  of  what  has  just  been  stated 
regarding  the  fibrous  tracts  of  the  posterior  spinal  roots  has  not,  with  certainty,  been 
ascertained  to  be  true  in  man.  As  far  as  they  have  been  sought,  though,  correspond- 
ing arrangements  have  been  found,  as  in  those  mammals  that  have  been  thoroughly 
examined. 

So  far,  therefore,  can  the  sensory  tracts  be  followed  into  the  cord:  As 
the  most  important  of  them  are  established,  first,  those  entering  the  posterior 
columns  and  ascending  in  them  toward  the  brain;  second,  those  ending  in 
Clarke's  vesiciilar  column;  third,  those — comprising  the  greater  mass  of  the 
lateral  root-fibers — which,  after  a  greater  or  less  course,  arborize  around 
cells  of  the  anterior  and  posterior  horns.  Besides  these  there  are  fibers 
known  which  pass  into  the  lateral  mixed  zone,  some  coming  from  the  an- 
terior horn,  some  going  to  it. 

As  to  those  fibers  which  arrive  at  the  posterior  horns  and  the  gray 
matter  just  in  front  of  these,  it  has  been,  in  all  probability,  determined  how 
they  enter  into  relationship  with  higher  centers.  From  the  ganglion-cells 
around  which  the  root-fibers  arborize  arises  a  second  set  of  fibers.  The  axis- 
cylinders  of  these  cells  turn  forward  and  inward  to  the  anterior  commissure, 
cross  over  in  it  to  the  anterior  or  lateral  column  of  the  opposite  side,  in  which 
they  ascend  farther.  What  portion  of  the  antero-lateral  column  is  really  to 


356  ANATOMY    OF    THE    CENTRAL   NERVOUS    SYSTEM. 

be  regarded  as  sensory  is  doubtful.  To  me  it  seems  most  probable  that  the 
sensory  fibers  are  here  spread  out  over  the  entire  cross-section  of  this  column. 
Still,  much  is  in  favor  of  the  view  that  the  anterior  radicular  zone  contains 
many  of  these  secondary  sensory  fibers. 

We  have  learned  of  two  kinds,  then,  of  extension  of  the  posterior  root- 
fibers:  one  direct  in  the  posterior  columns,  and  another  indirect,  which 
only  by  connecting  with  a  secondary  decussating  tract  takes  a  cerebral 
direction.  We  will  see  later  that  the  uncrossed  fibers  encounter  higher  up 
in  the  medulla  cells,  there  located,  and  then  cross  over;  so  that  the  whole 
tract  finally  decussates. 

It  were  scarcely  possible  to  draw  these  conclusions  regarding  the  pos- 
terior root-fibers  were  it  not  true  that  in  the  lower  vertebrates,  in  the  spinal 
cord,  the  relations  are  very  simple, — one  might  even  say  schematic.  After 
it  had  been  demonstrated  with  them  that  the  majority  of  their  posterior 
root-fibers  ran  into  a  central  gray  deposit  of  fibers  and  cells,  and  from  there 
new  tracts,  after  crossing,  extended  on  toward  the  brain,  it  was  but  a  step  to 
look  for  corresponding  conditions  with  man  and  mammals.  The  discovery 
by  Eamon  y  Cajal  that  the  posterior  root-fibers  split  up  around  the  cells  of 
the  spinal  gray  matter,  and  that  from  these  cells  there  came  out  a  tract 
which  crossed  over  in  the  anterior  commissure,  gave  to  the  supposition  some- 
thing of  definiteness. 

With  this  new  achievement  of  knowledge  coincide  well  the  results  of  experi- 
mental and  clinical  pathology.  If,  for  instance,  a  spinal  cord  were  cut  through  its 
lateral  half,  underneath  the  point  of  section  the  tactile  sense  would  be  lost, — not 
on  the  corresponding  side,  but  on  the  opposite  one.  This  datum  could  not  be 
reconciled  with  what  was  known  of  the  crossed  extensions  of  the  posterior  root- 
fibers  in  the  posterior  columns.  It  was,  however,  soon  cleared  up,  when  we  learned 
that  a  considerable  portion  of  such  a  root,  soon  after  its  entrance  into  the  cord, 
was  continued  by  a  secondary  tract  over  to  the  other  side. 

One  must  not  suppose  that  all  the  impulses  reaching  the  spinal  cord  by  the 
sensory  roots  are  identical  with  what  is  ordinarily  termed  "sensation."  In  order 
that  an  impression  be  perceived,  it  is  not  sufficient  that  it  be  conducted  to  the 
spinal  cord,  but  it  must  be  farther  carried  up,  from  the  place  Avhere  the  peripheral 
path  ends,  to  the  cerebral  cortex.  There  is,  however,  no  doubt  at  all  that  these 
higher  connections  are  few  in  number,  and  that,  contrasted  with  the  multitude  of 
fibers  in  the  posterior  roots,  the  number  of  such  central  connections  is  quite  small. 
This  alone  makes  the  conclusion  possible  that  there  are,  indeed,  many  sensory  im- 
pressions \yhich  arrive  at  the  spinal  cord,  but  that  we  are  aware  of  but  few  of  them 
at  the  time.  All  the  viscera  of  the  body,  as  the  silver  staining-method  has  distinctly 
shown,  are  traversed  by  an .  altogether  unexpectedly  large  number  of  nerves,  and 
their  arrangement  and  course,  their  relations  to  blood-vessels  and  glands,  and  to 
muscle-fibers,  bones,  and  enamel,  make  it  more  than  probable  that  there  is,  in  this 
connection,  a  large  system  which  serves  essentially  to  regulate  impressions  and  reflex 
action  (Exner).  This  is  often  overlooked  in  analyzing  the  results  of  section  of  cer- 
tain columns.  Until  lately  only  the  very  coarsest  qualities  of  sensation  have  been 
tested.  And  even  now,  when  we  know  so  much  better  than  formerly  the  anatomic 


THE    COURSE    OF    THE    FIBERS    IN    THE    SPINAL    CORD.  357 

relations  of  the  spinal-cord  tracts,  the  phenomena  revealed  by  physiologic  ex- 
periments are  to  be  very  carefully  interpreted;  but,  on  the  other  hand,  it  seems  to 
me  desirable  that  new  examinations  of  spinal-cord  sections,  whether  partial  or  total, 
be  made  in  man,  because,  with  the  lower  animals,  there  is  reaction  only  to  the  coarsest 
kind  of  impressions,  which  do  not  amount  to  actual  pain.  It  is  positively  known, 
so  far,  that  the  posterior  columns  do  not  conduct  those  impressions  which  in  the 
cortex  are  recognized  as  tactile,  and  it  is  quite  probable  that  these  are  farther  con- 
ducted by  the  portion  entering  into  the  gray  matter,  which  there  soon  connects  with 
its  secondary  extension.  With  these  fibers  must  also  be  found  the  central  paths 
conveying  impulses  of  temperature  and  pressure  sensations. 

In  the  posterior  columns  run,  presumably,  tracts  which,  partly  through  their 
cerebellar  connections  and  partly  through  their  cerebral  connections  with  the  so- 
called  cortical  motor  centers,  in  some  manner  influence  the  sensory  regulation  of 
movements  and  muscle-tone. 

There  remains  still  to  be  considered  that  part  of  the  posterior  root 
whose  fibers  arborize  around  the  cells  of  Clarke's  column.  It  has  probably 
nothing  to  do  with  the  conduction  of  tactile  impressions,  according  to  path- 
ological data.  The  secondary  tract,  or  prolongation  upward  from  Clarke's 
column,  does  not  join  with  the  general  sensory  paths.  From  these  cells  arise 
fibers  which  leave  the  gray  matter  laterally,  and  on  the  periphery  of  the 
gray  matter  enter  the  direct  cerebellar  tract.  With  it  they  pass  up  to  the 
cerebellum.  These  fibers  are  doubtless  important  for  the  co-ordination  of 
movements.  For  not  only  in  cerebellar  disease  are  gait  and  station  inco- 
ordinated,  but  also  in  tabes  dorsalis,  in  which  one  meets  with  ataxia  of  the 
highest  degree,  are  these  fibers  of  the  posterior  column  and  the  columna 
vesicularis  degenerated,  resulting  in  an  interruption  to  the  paths  leading 
to  the  cerebellum. 

The  anatomical  relations,  then,  which  are  affected  by  the  entrance  of 
the  posterior  nerve-roots  into  the  cord,  are  much  more  complicated  than  are 
those  of  the  anterior  roots.  We  have  already  seen  this  to  a  degree.  Prob- 
ably there  exist  still  other,  as  yet  unknown,  systems  of  fibers. 

The  relations  of  many  of  the  cells  of  the  ventral  and  dorsal  horns  to  the 
root-fibers  we  have  already  learned.  There  are,  in  the  gray  matter,  still 
many  cells,  which  do  not,  however,  stand  in  direct  relation  to  the  root-fibers. 
First,  there  are  cells  whose  axis-cylinders  do  not  pass  over  into  a  longitudinal 
bundle  or  into  a  root-fiber,  but  soon  after  their  soiirce  form  extremely  fine 
arborizations.  They  are  seen  everywhere  on  the  cross-section,  but  are  espe- 
cially noteworthy  in  the  border-region  of  the  dorsal  horn.  Then  there  have 
been  recognized  multipolar,  scattered  cells,  which  give  off  one  axis-cylinder 
in  the  corresponding  or  the  opposite  antero-lateral  tract  (Figs.  210  and  227). 
There  it  splits  into  an  ascending  and  a  descending  branch  (Fig.  220).  The 
branches  from  these  "tract-cells" .  extend  a  short  distance  in  the  antero- 
lateral  columns,  then  give  off  collaterals,  which  again  enter  the  gray  matter 
and  there  arborize  around  other  cells.  These  cells  unite  by  their  processes 


358  AXATOMY    OF    THE    CENTRAL    NERVOUS    SYSTEM. 

levels  of  the  cord,  which  lie  cephalad  or  caudad  from  them;  hence  the}-  are 
adapted  to  serve  as  a  substratum  for  the  long-accepted  paths  that  connect 
together  different  levels. 

To  any  irritation  coming  to  the  cord  from  the  periphery  there  are  offered  a 
large  number  of  conduction-paths.  There  is,  first  of  all,  a  number  of  posterior  root- 
fibers  which  extend  directly  into  the  anterior  horn  and  arborize  around  its  cells. 
These  are  well  adapted  to  "load"  such  cells  with  impressions,  or  after  sufficiently  high 
irritation  to  call  forth  immediate  discharge  of  motor  reflexes.  But,  through  cells 
originally  in  relation  with  each  other,  and  through  others  that  are  so  as  a  result  of 
selective  function,  the  motor  cell-groups  are  functionally  associated  in  such  a  man- 
ner that  a  single  impression  is  often  sufficient  to  bring  an  entire  group  of  cells  to 
discharge  at  the  same  time.  So  reflexes  may  consist  of  single  muscular  movements 
and  also  of  very  complicated  actions.  Besides  the  dendrites  the  "tract-cells"  with 
their  processes  form  the  anatomic  basis  of  these  associations.  It  is  not  difficult  to 
accept  the  statement  that  an  impulse,  arriving  at  the  spinal  cord,  spreads  in  this 
way  through  these  cells  over  different  levels,  and  so  unites  in  exciting  motor  cells 
of  the  most  varied  positions  to  simultaneous  action.  (Exner  and  others.) 

All  these  fibers  and  cell-processes  form  an  extraordinarily  complicated 
mesh-work  in  the  gray  matter  of  the  cord.  Its  unraveling  has  been  accom- 
plished only  by  the  use  of  all  the  methods  ever  conceived.  In  the  adult 
cord,  colored  after  the  Weigert  method,  this  is  impossible. 

All  fibers  crossing  from  one  side  to  the  other  occupy  either  the  anterior 
or  the  posterior  commissure. 

Although  the  component  elements  of  these  commissures  have  already  been  men- 
tioned, each  in  its  place,  still  it  will  be  well  to  consider  them  again  more  topographic- 
ally. 

In  the  anterior  commissure-,  then,  we  find    (Fig.  227) : — 

1.  Belonging  to  the  anterior  roots:    fibers  from  cells  to  the  opposite  root;    col- 
laterals  of  the   direct  pyramidal  tract;     numerous   dendritic   processes   from  neigh- 
boring ventral  horn-cells. 

2.  Secondary  sensory  paths  from  those  cells,  around  which  arborize  fibers  from 
the  posterior  nerve-roots. 

3.  From   the   "tract-cells":     numerous   axis-cylinder   processes  to  the   opposite 
anterior  and  lateral  columns. 

4.  Connecting  fibers  from  the  lateral  column  of  one  side  to  the  anterior  column 
of   the   other. 

This  tract,  found  by  Schaffer  in  vertebrates  of  different  classes,  is,  according  to 
him,  made  up  of  posterior  root-fibers,  which  first  enter  the  lateral  column,  and  higher 
up  cross  over  into  the  opposite  anterior  column.  It  has  been  demonstrated,  also,  in 
animals  that  have  no  medullary  pyramidal  fibers  (reptiles)  ;  therefore  it  cannot  be 
an  accessory  pyramidal  tract:  a  supposition  which  otherwise  might  seem  true. 

Of  the  posterior  commissure  we  know  much  less.  Of  a  certainty  it  con- 
tains medullated  fibers,  and  these  surely  arise  from  the  posterior  roots  and 
from  tracts  into  which  the  posterior  root-fibers  have  entered. 


THE    COURSE    OF   THE    FIBERS    IN    THE    SPINAL    CORD.  359 

In  the  fetus  of  different  mammals  different  dispositions  of  fibers  have  been 
found  in  this  commissure,  according  to  the  class  of  animal  examined.  In  the  dog, 
for  example,  three  divisions  of  these  commissural  fibers  can  be  distinguished;  in  the 
cow  only  two,  and  so  forth. 

As  far  as  the  anatomic  relations  of  the  component  tracts  of  the  spinal  cord 
could  be  determined  macroscopically,  Burdach,  Sommering,  and  J.  Arnold  rendered 
important  service.  Bellinger!  was  the  first  to  recognize  the  connection  between  the 
gray  matter  of  the  ventral  horns  and  the  anterior  nerve- roots;  Grainger,  that  be- 
tween the  dorsal  horns  and  the  posterior  nerve-roots.  The  minute  structure  of  the 
cord  was  first  revealed  by  B.  Stilling,  later  Kolliker,  Goll,  Deiters,  Gerlach,  Clarke, 
and  others  have  added  to  our  knowledge  of  it.  To  the  labors  of  Tiirck,  Flechsig, 
Charcot,  and  Gowers  we  are  indebted  for  the  major  part  of  our  ideas  of  the  dis- 
position of  the  fibers  of  the  white  matter.  Within  more  recent  times,  however, 
through  the  advances  made  by  His,  Golgi,  and  S.  Ramon  y  Cajal  (collaterals,  arbor- 
ization of  axis-cylinders,  etc.),  through  the  researches  of  Kolliker,  Van  Gehuchten, 
and  Lenhossek,  of  whom  mention  has  already  been  made  in  the  introductory  chapter, 
a  very  important  gain  has  been  made  in  our  knowledge  of  the  spinal  cord.  Besides 
them,  Singer  and  Miinzer,  Lowenthal,  Mott,  and  others  have  cleared  up  much  that 
was  not  understood,  and  we  are  indebted  to  Waldeyer  for  a  critical  revision  of 
accumulated  data,  together  with  many  new  subjects. 

One  might  carry  the  study  of  the  most  important  fiber-systems  in  the 
cord  much  farther,  going  into  many  interesting  details.  But  we  have  already 
found  so  many  places  where  uncertainty  prevails  that,  adhering  strictly  to 
the  limits,  beyond  which  one  finds  only  a  complex  of  details  and  contra- 
dictory opinions  of  authors,  we  need  hardly  pursue  it  farther. 

In  the  introduction  to  his  great  work  on  the  structure  of  the  spinal 
cord,  Stilling  says:  "We  must  not  forget,  following  in  the  train  of  the  noble 
Burdach,  that  in  the  examination  of  the  spinal  cord  we  are  exploring  a 
wonderland,  which  we  know  very  little  about;  and  we  may  only  gaze  at  the 
rivers  and  mountains,  to  get  a  clear  general  understanding  of  the  whole, 
leaving  to  our  successors  to  explore  every  brook  and  to  seek  out  every 
height." 

Thirty-six  years  have  passed  since,  with  these  prefatory  words,  one  of 
the  most  valuable  books  appeared  with  which  the  anatomic  department  of 
science  has  been  enriched,  and  to-day  we  are  still  far  from  the  goal;  it  will 
be  long  still  before  that  field-map  will  be  completed,  of  which  Burdach  and 
Stilling  dreamed. 

In  the  cord  there  lie  in  close  proximity  to  each  other,  physiologically  widely 
differentiated  fibers;  the  cells,  which  may  be  regarded  as  central  cells,  are  thickly 
surrounded  by  peripheral  conducting  paths.  It  is  clear  from  this  that  it  is  very 
difficult  to  learn  the  results  and  to  establish  the  symptoms  which  appear  upon  dis- 
ease or  lesion  of  any  of  these  component  parts  of  the  cord. 

Still,  close  observations  at  the  sick-bed  and  at  autopsies  have  taught  much 
in  this  connection.  A  number  of  spinal-cord  diseases  affect  invariably  certain  por- 
tions of  the  cord,  always  certain  tracts  or  particular  groups  of  ganglion-cells,  and 
leave  the  other  tracts  of  the  cross-section  intact,  forever  or  for  a  long  time.  The 


360  ANATOMY    OF   THE    CENTRAL   NERVOUS    SYSTEM. 

observation  of  such  forms  will  be  of  prime  importance  for  the  question  confronting 
us.  We  also  discover  much  as  the  result  of  wounds,  sections  and  compressions  of  the 
cord,  as  often  arise  from  caries  of  the  vertebrae,  and  tumors. 

Much  less  effective  than  pathology  is  the  examination  of  animals.  Compared 
with  pathologic  processes  occurring  in  the  fine  mechanism  they  affect,  the  neces- 
sary experimental  attempts  are  exceedingly  coarse  and  bungling. 

We  cannot,  of  course,  in  this  work  give  even  a  short  resume  of  the 
valuable  finds  for  which  we  are  indebted  to  numerous  researches  made  in  the 
pathology  of  the  spinal  cord.  There  are  many  excellent  works  in  this  line. 

Only  a  few  especially  important  and  well-established  points  should  be 
here  mentioned. 

Disease  of  the  posterior  columns  causes  different  symptoms  according 
to  its  location  in  them.  Destruction  of  the  entering  posterior  roots  must 
interrupt  the  entire  sensory  apparatus  they  contain,  entailing  the  loss  not 
only  of  every  quality  of  sensation,  but  also  of  the  reflexes,  which,  indeed, 
are  possible  through  the  sensory  paths.  Then,  also,  the  tendon-reflexes 
disappear.  Those  degenerations  of  the  posterior  columns  which  do  not  affect 
the  entering  nerve-roots,  or  do  so  but  partially,  run  their  courses  without 
special  disturbance  of  cutaneous  sensibility,  although  the  muscular  sense 
seems  invariably  to  suffer.  The  motor  power  is  in  nowise  affected  by  disease 
of  these  columns. 

If  the  gray  matter  of  the  ventral  horns  be  destroyed  by  a  disease-process 
there  ensues,  as  in  the  case  of  destruction  of  peripheral  nerves,  paralysis  of 
the  muscles  which  derive  their  nerve-supply  from  the  respective  level  of  the 
cord.  To  this  paralysis  is  quickly  added  atrophy  of  the  paralyzed  muscles. 
In  this  respect  does  it  also  resemble  peripheral  paralysis:  viz.,  that  the  par- 
ticular muscles  react  to  the  electric  current  exactly  as  if  the  supplying  nerve 
were  severed.  Since  the  nerve  and  its  end-organ  in  the  muscle  are  but  proc- 
esses of  the  cell,  it  is  not  difficult  to  understand  this  relation. 

From  the  last-described  symptom-complex  one  will  always  be  able  to 
diagnose  an  affection  of  the  lower  segment  of  the  motor  path. 

Entirely  different  signs  appear  if  there  be  an  interruption  in  the  upper 
segment  of  the  motor  path,  the  tractus  cortico-spinalis. 

If  the  pyramidal  tracts  are  diseased,  voluntary  movements  are  dis- 
turbed or  lost.  In  addition,  the  paralyzed  muscles,  or  those  which  may  be 
only  slightly  weakened,  show  a  permanent  increase  in  tension,  tend  toward 
contractures,  and  are  much  more  irritable  to  mechanical  stimuli  than  nor- 
mally. Always,  in  the  presence  of  these  symptoms  alone,  or  when  met  with 
in  conjunction  with  other  symptom-complexes,  one  can,  with  entire  cer- 
tainty, accept  the  fact  of  a  participation  of  the  pyramidal  tracts  in  the 
disease.  Not  seldom  has  unilateral  interruption  to  the  pyramidal  fibers  been 
followed  by  bilateral  paresis  and  increase  of  muscular  tension. 

There  occur  diseases  of  the  primary  (lower)  and  secondary  (upper) 


THE    COUESE    OF   THE    FIBERS    IN    THE    SPINAL   COED. 


361 


motor  tracts  in  combination.  Of  these  the  best  observed  is  the  amyotrophic 
lateral  sclerosis.  Here  the  clinical  signs — paresis,  spasms,  muscular  atrophy 
— correspond  to  the  anatomic  condition:  disease  of  the  pyramidal  tracts 
and  of  the  ventral  horn-cells. 

These  relations  are  readily  understood  by  a  glance  at  the  preceding 
schematic  representation  (Fig.  229).  A  lesion,  located  in  the  line  x  a  c  (i.e., 
in  the  fibers  it  represents),  produces  paralysis.  If  it  interrupt  this  line  above 


Hirnnnde, 


Fig.  229. — Schema  of  innervation  of  a  muscle.    Hirnrinde,  Brain-cortex.    Vorder- 
hornzelle,  Cell  of  ant.  horn.     Vorderuwrzel,  Anterior  root. 


the  ganglion-cell,  as  at  x  or  a,  it  assumes  the  character  of  a  central  paralysis, 
without  atrophy,  and  eventuates  often  in  improvement  or  cure,  probably 
through  the  substitution  of  other  paths  for  those  represented  by  x  a.  If, 
however,  the  line  x  a  c  be  broken  at  the  ganglion-cell  or  anywhere  in  c,  then 
there  follows  not  only  paralysis,  but  also  wasting  of  the  paralyzed  nerves,  and 
atrophy  of  their  corresponding  muscles.  As  a  consequence,  the  outlook 
toward  recovery  in  the  paralyzed  members  is  very  slight.  At  times  after  a 


362  ANATOMY   OF   THE    CENTRAL    NERVOUS    SYSTEM. 

long-continuing  lesion  of  x  a,  there  ensues  gradual  participation  of  the  part 
c.  But  this  occurs  seldom.  Interruption  of  the  path  a  leads  to  'descending 
degeneration  from  the  point  of  lesion  to  the  level  of  the  respective  ventral 
horn. 

As  an  example  of  paralysis  and  muscular  atrophy,  occurring  with 
disease  of  the  ventral  horns,  may  be  mentioned  "infantile  spinal  paralysis." 
In  this  affection  complete  paralysis  of  single  muscle-groups  occurs  suddenly, 
and  there  follows  very  quickly  wasting  of  the  muscular  tissue.  Examina- 
tion of  the  spinal  cord  reveals  then  disease-foci  in  the  gray  matter  of  the 
ventral  horns.  The  nerves  also,  as  well  as  the  anterior  nerve-roots,  atrophy 
gradually. 

We  do  not  yet  possess  sufficiently  exact  evidence  to  be  able  to  say  what 
symptoms  arise  from  disease  of  the  gray  matter  of  the  dorsal  horns.  But 
from  the  analysis  of  cases  of  tabes  dorsalis,  in  which  they  were  spared,  and 
of  those  in  which  they  were  affected,  we  may  conclude  that  lesions  involving 
them  lead  probably  to  disturbances  of  cutaneous  sensibility,  and  particularly 
to  trophic  changes  in  the  skin.  In  syringomyelia  and  with  tumors  located 
within  the  gray  matter  among  other  disturbances  appear  those  of  tempera- 
ture and  pain-sense. 


CHAPTER    XXIII. 

THE   MEDULLA   OBLOXGATA. 

AT  the  upper  end  of  the  spinal  cord  the  white  fibers  of  which  it  is  made 
up  are  disposed  in  various  ways,  the  extent  and  form  of  the  gray  matter 
changes  considerably,  new  deposits  of  neuroglia  and  of  ganglion-cells  appear, 
and  the  well-known  picture  of  the  cross-section  of  the  spinal  cord  rapidly 
disappears;  especially  is  it  indistinct  when,  at  the  upper  segment  of  the  cord, 
right  and  left,  there  where  the  lateral  tracts  were,  the  inferior  olive  arises, — 
a  gray,  much  folded,  richly  cellular  layer, — and  when  the  central  canal, 


H'mterhorn. 


.-:}£.    lessor 


Ract.ant  A*cm>.  I. 


Fig.  230. — Section  through  the  upper  cervical  cord.  Hinterhorn,  Posterior 
horn.  Proc.  reticularis,  Association-field.  Seitetihorn,  Lateral  horn.  Rad.  ant. 
N.  cert).  I,  Ant.  root  of  I  cervical  nerve. 

approaching  more  and  more  nearly  to  the  dorsal  surface,  expands  into  the 
fourth  ventricle. 

The  series  of  transverse  sections  here  presented  is  intended  to  explain 
the  evolution  of  the  medulla  oblongata  out  of  the  spinal  cord. 

Fig.  230  represents  a  section  of  the  cervical  cord,  corresponding  to  that 
part  from  which  passes  the  first  cervical  nerve.  It  but  recalls  the  relations 
as  already  described  in  the  preceding  chapter.  Three  points,  however,  dis- 
tinguish it.  The  first  is  the  peculiar  form  of  the  posterior  horn,  which  is 

(363) 


364 


ANATOMY    OF    THE    CEXTKAL    NERVOUS    SYSTEM. 


connected  only  by  a  thin  "neck"  with  its  dorsal  extremity,  here  greatly 
thickened  by  substantia  gelatinosa,  forming  the  "head  of  the  dorsal  horn/' 

Through  the  substantia  gelatinosa  pass  numerous  fine  fibrils,  which  are  partly 
posterior  root-fibers.  Another  portion  of  them  comes  from  a  greater  distance,  namely 
from  the  Gasserian  ganglion.  The  cells  of  this  ganglion  emit  peripherally  the  nermis 
trigeminus,  and  centrally  the  trigeminal  root.  A  part  of  these  latter  fibers  turn 
downward,  and  from  them  pass  continuously  fine  fibrils  to  the  end-nucleus  of  the 
trigeminus:  a  column  of  gelatinous  substance,  which  is  demonstrable  from  the  pons 
down  to  the  substantia  gelatinosa  of  the  upper  cervical  cord.  The  crescentic  trans- 
verse section  of  the  tractus  spinalis  of  the  fifth  nerve  lies  in  the  cervical  cord  in  close 


Fig.  231. — Cross-section  of  the  oblongata  through  the  pyramidal  decussa- 
tion.  Fpy,  Pyramidal  tract.  Cga,  Anterior  horn.  Fa',  Remnant  of  anterior 
column.  Ng,  Nucleus  funiculi  gracilis.  g,  Substantia  gelatinosa.  XI,  Nervus 
accessorius.  (After  Henle.) 


proximity  to  the  substantia  gelatinosa,  as  in  the  oblongata  and  the  pons.  It  can  be 
seen  in  all  the  sections  hereafter  represented  (Figs.  232  and  238,  for  example).  It 
has,  until  now,  been  called  the  ascending  root  of  the  fifth  nerve  (see  also  Fig.  251). 

Further  one  finds  the  lateral  horns  here  well  developed.  From  cells 
lying  at  their  bases  and  higher  up,  appearing  on  the  lateral  edge  of  the  an- 
terior horn,  comes  the  nervus  accessorius  Willisii.  Its  root-fibers,  which 


THE    MEDULLA   OBLOXGATA.  365 

arise  below  as  far  as  the  sixth  cervical  nerve,  and  above  as  far  as  the  be- 
ginning of  the  oblongata,  do  not  arise  in  exact  order,  as  might  appear  from 
Fig.  230,  but  extend  first  toward  the  brain,  and  later  they  bend  outward 
forming  a  knee  (Darkschewitsch).  Only  the  horizontal  limb  of  this  knee 
has  been  caught  in  this  section,  represented  in  Fig.  230. 

The  most  anterior  fibers  of  the  accessorius  in  animals,  and  in  one  case  observed 
in  man,  contain  the  inhibitory  fibers  to  the  heart.  I  have  seen  pronounced  slowing 
of  the  pulse  on  defecation  arise  from  the  existence  of  a  varix  in  the  frontal  ac- 
cessorius region,  and  I  saw  this  patient  die  with  symptoms  of  increasing  slowing  of 


Fpy 

Fig.  232. — Cross-section  of  the  oblongata  in  the  region  of  the  lowest  hypo- 
glossal  roots.  The  pyramidal  decussation  nearly  complete.  Nc,  Nucleus  funiculi 
cuneati.  XII,  Nervus  hypoglossus.  Other  marks  same  as  in  Fig.  231.  (After 

Henle.) 

the  heart's  action,  when  the  varix  became  larger  and  finally  burst.     (Berliner  klinische 
Wochenschrift,  1898.) 

Notice  also,  that  in  the  space  between  the  anterior  and  posterior  horns 
the  gray  matter  passes  through  the  lateral  column  in  the  form  of  a  com- 
plicated net-work;  this  is  the  formation  of  the  processus  reticulares. 

Their  gray  matter  consists  almost  exclusively  of  commissural  cells, 


366  ANATOMY    OF   THE    CENTRAL    NERVOUS    SYSTEM. 

which  join  the  different  levels  together.  Earlier  in  this  work,  in  the 
consideration  of  the  brains  of  lower  animals,  attention  was  called  to  the 
fact  that  regularly  at  the  border  between  the  spinal  cord  and  the  bulb  this 
great  commissural  system  appears,  or  strengthens  that  already  existing.  It 
was  there  designated  as  the  association-field  of  the  medulla. 

Above  the  level  just  described  begins  the  rearrangement  of  fibers,  etc., 
which  brings  about  the  changes  observed  in  the  cross-section  of  the  bulb. 

We  have  learned  in  the  cord  of  two  fasciculi  cortico-spinales,  one  of 
which,  lying  in  the  anterior  column,  conducts  toward  the  brain  fibers  which 
are  derived  on  the  opposite  side  from  all  the  different  root-regions,  and  a 
second,  the  crossed  pyramidal  tract,  which  contains  fibers  from  the  cor- 
responding ventral  horn. 

At  the  upper  end  of  the  cord  this  latter  tract  enters  the  anterior  column 
of  the  opposite  side,  by  large  bundles,  which  break  through  the  ventral  horn 
of  the  same  side.  There  it  meets  the  anterior  or  direct  pyramidal  tract,  and 
beyond  this  the  uncrossed  tractus  cortico-spinalis  passes  with  the  crossed  as 
pyramidal  tract  to  the  brain.  The  dorsal  horns  move  farther  forward,  just 
as  the  place  in  the  lateral  column  occupied  by  the  crossed  pyramidal  tract 
becomes  free. 

A  few  millimeters  higher  still  the  pyramidal  decussation  is  complete. 
There  lie,  then,  now  the  crossed  p3Tamidal  fibers  with  the  direct  pyramidal 
fibers  in  one  large  bundle,  ventral  in  the  medulla.  This  is  distinctly  shown 
in  Fig.  232.  It  will  be  seen,  too,  that  the  anterior  ground-bundle  (Fa')  is 
placed  dorsal  to  the  pyramids.  External  to  the  separated  remnants  of  the 
ventral  horn  a  small  gray  focus  is  seen.  It  belongs  to  the  lowest  point  of  the 
olivary  body.  The  olive  enlarges  materially  as  one  ascends,  and  fills  a  large 
part  of  the  room  in  the  lateral  tracts.  These  latter,  from  the  appearance  of 
the  processus  reticulares,  have  become  richer  in  fibers.  The  association-field 
develops  more  and  more.  However,  the  paths  are  only  traceable  a  short  dis- 
tance. Many  end  in  scattered,  small  groups  of  ganglion-cells  (nucleus  of  the 
lateral  tract,  nucleus  reticularis  tegmenti,  etc.). 

The  rearrangement  of  fibers,  the  crossing  of  the  lateral  pyramidal  tract 
over  to  the  opposite  anterior  column,  is  well  shown  in  the  accompanying 
drawings  by  Henle  (Figs.  231  and  232).  The  separated  ventral  horns  can  be 
traced  farther  upward,  but  disappear  at  about  the  level  of  the  pons. 

The  pyramidal  tracts  are  seen  on  all  the  following  sections,  lying  be- 
tween the  olivary  bodies  anteriorly  (see  illustrations  in  following  chapter). 
Later  they  are  covered  over  and  divided  into  bundles  by  the  transverse  fibers 
of  the  pons.  How  they  emerge  farther  on  beyond  the  pons  and  pass  through 
the  pes  cerebri  into  the  internal  capsule  has  been  repeatedly  described  in 
preceding  chapters.  It  has  also  been  explained  that  the  secondary  degener- 
ation, which  takes  place  downward  after  interruption  to  the  cortico-spinal 


THE    MEDULLA    OBLONGATA. 


367 


tract  in  the  brain,  affects  in  the  bulb  the  posterior  part  of  the  opposite  lateral 
column  and  the  anterior  column  of  the  same  side. 

Opportunity  to  follow  the  course  of  the  pyramidal  tract  is  offered  not  so  seldom, 
if  in  autopsies  on  cases  of  long  standing  cerebral  unilateral  paralysis  one  make 
transverse  sections  of  the  pes  cerebri,  the  pons,  the  bulb,  and  the  cord.  The  gray 
pyramid  of  the  diseased  side  appears  usually  in  marked  contrast  to  the  white  fibers 
of  the  other  side;  in  the  cord  a  grayish  spot  is  noticeable  in  the  posterior  part  of 
the  opposite  lateral  column. 

At  the  level  of  the  pyramidal  decussation  appear  also  changes  in  the 
dorsal  columns.  In  their  centers,  first  in  the  postero-median,  later  in  the 


m  \#&.  •••: 
P  mM  \ 


Fig.  233. — Section  through  the  beginning  of  the  oblongata  ot  a  human  em- 
bryo at  the  twenty-sixth  week  of  gestation.  One  sees  the  fibers  going  from 
Burdach's  column  to  the  decussation  of  the  fillet,  and  the  fibrse  arciformes  ex- 
ternse  dorsales  from  Coil's  column,  later  described.  Notice  the  position  of  the 
cerebellar  tract.  Hinter,  Vorder  Horn,  Post.,  Ant.  horn.  Oliv.  Zwisch.  Schicht, 
Interolivary  layer.  Vorder-Strany-Rest,  Remains  of  ant.  column. 


postero-lateral  tracts,  arise  groups  of  gray  deposits,  containing  ganglion- 
cells:  the  nucleus  gracilis  and  the  nucleus  cuneatus.  These  nuclei  blend 
with  the  gray  matter,  whose  form  is  correspondingly  altered.  (In  Fig.  231 
the  first  of  these  may  be  seen;  in  Fig.  232  both  of  them.) 


368  ANATOMY   OF   THE    CENTRAL    NERVOUS    SYSTEM. 

Probably  all  the  fibers  of  the  posterior  columns  ultimately  end  in  these 
nuclei.  From  them,  in  turn,  spring  masses  of  fibers  through  the  gray  matter 
forward,  and  cross  over  to  the  other  side  anterior  to  the  pyramidal  crossing. 
These  fibers  later  make  up  the  fillet,  hence  this  crossing  is  called  the  decus- 
sation  of  the  fillet. 

It  is  not  very  easy  to  be  convinced  of  the  existence  of  a  fillet-crossing  in  a 
fully-developed  brain.  But  there  remains  no  doubt  at  all,  when  one  examines  sec- 
tions of  the  bulb  in  a  fetus  of  seven  months.  There  the  medullary  fibers  of  the 
pyramidal  decussation  do  not  yet  disturb  the  picture,  the  fibers  of  the  posterior  tracts 
being  more  distinct  through  being  earlier  provided  with  medullary  sheaths.  At  first 
one  sees  principally  only  fibers  coming  from  the  nucleus  cuneatus;  toward  the  ninth 
month,  however,  a  little  higher  up,  one  may  recognize  the  decussating  fibers  from 
the  nucleus  gracilis. 

Comparing  Fig.  233  with  the  two  figures  preceding  it,  one  notices 
behind  the  central  canal  the  gray  matter,  much  wider  than  before.  In 
the  column  of  Goll  is  seen  its  nucleus;  also  in  the  column  of  Burdach 
its  nucleus;  both  are  continuous  with  the  gray  matter.  External  to  them, 
surrounded  by  a  thin  layer  of  medullated  fibers  (spinal  root  of  the  tri- 
geminal  nerve),  lies  the  substantia  gelatinosa  of  the  dorsal  horn.  In  front 
of  it,  in  the  space  which  in  Fig.  232  is  occupied  by  the  dark  pyramidal 
fibers,  is  a  clear  place,  because  these  fibers  have  not  yet  received  their 
medullary  sheaths.  The  anterior  ground-bundle  and  the  cerebellar  tracts 
lying  at  the  periphery  of  the  lateral  column  are  already  medullated. 

From  the  nuclei  of  the  posterior  columns  may  be  seen  issuing  fibers 
which  pass  in  curves  (fibres  arciformes  internee)  through  the  gray  matter, 
decussate  in  front  of  the  central  canal,  and  dispose  themselves  in  a  thick 
layer  dorsal  to  the  previously  decussated  pyramids.  The  territory  occupied 
by  them  corresponds  to  the  anterior  ground-bundle  of  the  cord.  The  major 
portion  of  the  fibers  ascending  in  these  already  decussated  sensory  tracts  are 
hereby  pushed  backward  and  outward  by  these  newly  arrived  fibers.  There- 
fore, the  united,  crossed,  sensory  paths  of  the  second  order  (secondary 
neurons)  gradually  fill  up  all  the  space  lying  between  the  two  new  gray 
masses,  which  arise  in  this  level  of  the  medulla  oblongata,  the  olives  (olivce 
inferior  es).  The  higher  one  goes  in  the  oblongata,  the  poorer  in  fibers  be- 
come the  posterior  columns.  Gradually  they  all  pass  by  the  arcuate  fibers 
into  the  fillet-crossing,  and  so  to  the  opposite  side,  near  the  median  line, 
where  they  form  the  interolivary  bundle,  or,  as  we  from  now  on  may  know  it, 
the  fillet,  for  its  fibers  pass  upward  to  the  fillet  of  the  midbrain  (lemniscus). 

In  Fig.  235  is  presented  a  scheme  of  the  course  of  the  sensory  fibers. 
One  may  trace  the  direction  of  each  bundle  by  it,  beginning  at  the  entrance 
of  the  root-fibers,  and  finally  demonstrate  where  each  one  ends  in  the 
medulla  oblongata.  Especially  noteworthy  is  it  that  the  fibers  which  have 


THE    MEDULLA    OBLONGATA. 


369 


decussated  in  the  cord  lower  down  are  joined  by  those  which  here  cross  over, 
forming  one  bundle. 

There  are  then,  in  this  region  of  the  bulb,  two  important  decussations: 


.    AW/A    , 
fjwtiM  f 


-T 


5^ 

*'^--^      5i-f. 

p^»»:. 

•Vj 

J         .'.¥.1. 

<>• 

gi^ 

^ 

~->'v' 

V?           X   ' 

>~—  —  *§• 

\  \          . 

,    \\   V 

--_—-"  ijv$ 

—  -"   ^ 
v?^ 

\N^K 
^ 

*?A 

^~^j^ 
^•'^\ 

./ 

§"'  -®l 

W  P 


1          ' 


Fig.  234.— Cross-section  through  the  medulla  oblongata  of  an  embryo  of 
twenty-six  weeks.  The  medullated  fibers  stained  with  haematoxylin.  The  left 
interolivary  tract  and  the  tractus  spinalis  .nervi  trigemini  are  not  shown.  In 
the  restiform  body  only  the  spinal  portion  is  medullated.  Fibne  arciformes, 
Fibr.  arc.  ext.  ant.  The  fibr.  arc.  ext.  post,  are  above,  to  the  left  and  externally, 
between  the  restiform  body  and  the  posterior  column.  The  bundle  marked 
"Seitenstrang"  is  the  tractus  cerebello-spinalis  ventralis  lateralis,  which  remains 
in  this  location  as  high  up  as  the  anterior  part  of  the  pons;  the  tract,  cerebello- 
spin.  dorsalis,  as  here  seen,  leads  direct  to  the  corpus  restiforme.  Oliven  Zwischen- 
schicht,  Interolivary  layer.  Inn.  Neben  Olive,  Internal  accessory  olivary  nucleus. 
Hint.  Neben  Olive,  Posterior  accessory  olivary  nucleus.  Hinterstrang,  Posterior 
column.  Seitenstr.  Bahn.,  Lateral  cerebellar  tract. 


370 


ANATOMY    OF    THE    CENTRAL    NERVOUS    SYSTEM. 


that  of  the  pyramids  and  that  of  the  fillets.    In  the  former  are  motor  fibers, 
in  the  latter,  fibers  serving  to  conduct  sensory  impressions. 

Two  new  fiber-areas  have  arisen:  ventrally  the  pyramidal  bundle  and 
dorsally  from  it  the  fillet.  We  will  be  able  to  follow  them  both  higher  up  to 
the  region  of  the  corpora  quadrigemina. 


Fig.  235. — Schema  of  the  course  of  the  sensory  fibers  from  the  posterior 
roots  up  to  the  medulla  oblongata.  Kleinhirn-Seiten  B.,  Lateral  cerebellar  tract. 
Vorder  Seitenstr.,  Antero-lateral  column. 


The  fillet  contains  many  more  fibers  in  adult  man  than  appear  in  the 
specimen  from  the  fetus,  just  demonstrated.  With  the  latter  all  the  fibers 
from  the  antero-lateral  ground-bundle  belonging  to  the  sensory  tract  are,  as 


THE    MEDULLA    OBLOXGATA. 


371 


yet,  non-medullated,  and  only  those  appear  distinctly  which  arise  from  the 
nuclei  of  the  posterior  columns. 

By  reason  of  the  two  decussations  the  appearance  of  the  cross-section 
changes  materially.     In  addition,  the  gray  matter,  as  presently  to  be  de- 


Fig.  230. — The  hind-  and  after-  brain  exposed  by  removal  of  their  roof. 
Velum  medullare  anticum  and  cerebellum  still  visible.  Velum  medullare  posti- 
cum  has  been  removed  along  the  dotted  line,  &a.  Zwischenhirn,  Thalamen- 
cephalon.  Mittelhirn,  Mesencephalon.  Hintcrhirn  and  Kleinhirn,  Pons  and  cere- 
bellum. Nachhirn,  Medulla  oblongata.  Riickenmark,  Spinal  cord.  Hirnschenkel, 
Cerebral  peduncle.  Bindearm,  Peduncle  of  cerebellum. 


scribed,  also  changes  its  form,  and  new  masses  of  it  appear  in  the  medulla; 
three  of  these — the  two  posterior  nuclei  and  the  olive — we  have  already 


372 


ANATOMY    OF    THE    CENTRAL   NERVOUS    SYSTEM. 


studied.  Above  all,  however,  the  external  form  of  the  medulla  is  greatly 
changed.  As  the  fibers  of  the  posterior  columns  gradually  run  into  their 
respective  nuclei  and  end  in  them,  the  gray  matter  of  these  nuclei  become 
more  and  more  exposed  and  finally  lie  on  the  dorsal  surface  of  the 
bulb.  But  the  posterior  columns  at  this  level  separate  gradually  from  each 
other.  This  brings  the  posterior  or  gray  commissure  of  the  cord  distinctly 
into  view,  where  these  columns  separate.  Here,  also,  the  central  canal 
broadens  and  forms  the  fourth  ventricle.  "What  covers  it  becomes  thinner 
and  more  expanded,  and  can  be  followed  as  far  as  the  cerebellum,  being 


AT.  cent 


Fig.    237. — Medulla    oblongata,    pons,    cerebellum,    and    pes    pedunculi    (anterior 
view) ;    to  demonstrate  exits  of  cranial  nerves. 


called  the  velum  medullare  posticum.    With  the  commissure  this  forms  the 
roof  of  the  fourth  ventricle. 

In  the  longitudinal  section  represented  in  Fig.  206  can  be  seen  the 
combined  coverings  of  the  fourth  ventricle,  namely:  the  velum  medullare 
posticum,  the  cerebellum,  and  the  velum  medullare  anticum.  Close  to  the 
beginning  of  the  fourth  ventricle,  in  the  velum  medullare  posticum,  is  an 
opening,  or  foramen,  leading  into  the  ventricle  from  without.  This  is  the 
foramen  of  Majendie,  already  mentioned,  through  which  the  fluid  in  the 
ventricle  communicates  with  that  which  flows  about  the  entire  central  nerv- 
ous system  in  the  subarachnoid  spaces. 


THE    MEDULLA   OBLOXGATA. 


373 


In  Fig.  236  this  entire  roof  is  represented  as  having  been  removed, 
allowing  free  view  into  the  fourth  ventricle.  Its  floor  is  bounded  below  by 
the  diverging  posterior  columns,  above  by  the  superior  cerebellar  peduncles, 
which  converge  toward  the  corpora  quadrigemina.  This  gives  it  its  peculiar 
diamond  shape. 

In  this  figure  the  view  of  the  medulla  posteriorly  indicates  the  gradual 
disappearance  of  the  posterior  columns  as  they  ascend,  and  that  in  place  of 
them  the  inferior  cerebellar  peduncles,  the  restiform  bodies  (see  below), 
appear.  The  protuberance  in  the  upper  part  of  the  posterior  median  column 
is  called  the  clava;  it  arises  from  the  deposit  of  the  nucleus  funiculi  gracilis. 

An  anterior  view  of  the  medulla  (Fig.  237)  shows,  first,  the  thick  swell- 


Fig.  238. — Section  through  the  oblongata  at  the  level  of  the  posterior  hyp- 
roots  (schematic).  Hiiiterstriiiiye,  Posterior  columns.  Hinterhorn, 
Posterior  horn.  Yorder-Seitenhorn,  Antero-lateral  horn.  Cereb.  Bahn,  Lateral 
cerebellar  tract.  Aus  Ruckenmark,  From  the  spinal  cord.  Aus  H.  Str.  Kernen, 
From  the  nuclei  of  the  posterior  columns.  Schleife,  Fillet. 


ing  of  the  pyramids,  arising  out  of  the  cord.  External  to  them  appear  the 
olivary  bodies,  at  the  head  of  the  lateral  columns,  as  two  large  tumefactions. 
A  little  higher  up  the  large  transverse  fibers  of  the  pons  apply  themselves 
across  in  front  of  the  pyramids.  In  the  extension  of  the  anterior  radicular 
groove  upward,  between  the  olive  and  the  pyramid,  arises  the  nervus 
hypoglossus  (XII]  from  the  medulla.  The  nervus  accessorius  Willisii  (XI} 
arises  from  the  cervical  cord,  and  higher,  from  the  medulla,  external  to 
the  olive,  by  numerous  small  bundles.  Above,  in  the  same  groove  ex- 


374  ANATOMY   OF   THE    CEXTRAL   XERVOUS    SYSTEM. 

tended,  the  nervus  vagus  (X}  and  the  nervus  glosso-pharyngeus  (IX} 
have  their  exit  from  the  medulla.  Just  behind  the  pons,  and  laterally, 
are  the  origins  of  the  nervus  acusticus  (VIII)  and  the  nervus  facialis 
(VII).  The  sixth  cranial  nerve,  the  abducens,  arises  internally  from  the 
two  last  named.  From  deep  in  the  pontile  fibers  springs  the  trigeminus 
(V).  The  origins  of  the  trochlearis  (IV)  and  the  oculo-motorius  (III)  we 
have  already  learned.  The  trochlear  comes  from  the  velum  medullare  an- 
ticum  behind  the  corpora  quadrigemina;  the  motor  oculi  ventrally  from 
the  pes  cerebri. 

The  last  section  of  the  medulla  considered  was  at  that  level  where  the 
central  canal  expands  into  the  fourth  ventricle.  Even  before  this  the  first 
nuclei  of  the  cranial  nerves  have  appeared  in  the  gray  matter  surrounding 
it.  The  fibers  of  the  accessorius  arise  from  cells  in  the  most  lateral  portion 
of  the  ventral  horn,  and  from  a  place  anterior  to  it,  which  corresponds  to 
the  base  of  the  former  anterior  horn,  the  nucleus  lujpoglossi,  the  fibers  of  the 
hypoglossal  nerve  develop. 

In  the  two  accompanying  figures  this  is  represented.  If  it  be  noticed 
how  the  central  canal,  following  the  separation  of  the  posterior  columns, 
spreads  out  and  becomes  the  fourth  ventricle,  it  will  then  be  easily  under- 
stood that  from  this  point  on  all  the  nerve-nuclei  must  lie  in  the  floor  of 
this  ventricle.  This  is  clearly  shown  in  Fig.  239.  Laterally  from  these 
centers  lie  the  posterior  columns,  now  sparsely  provided  with  fibers.  The 
posterior  horn,  discernible  by  the  substantia  gelatinosa  of  its  head,  is 
entirely  separated;  and  the  basal  part  of  the  lateral  horn,  too,  from  which 
come  the  fibers  of  the  motor  accessorius,  loses  its  connection  with  the  com- 
pact gray  matter  a  little  higher  than  the  plane  of  the  figure.  It  continues 
as  a  column  rich  in  ganglion-cells  ventral  to  the  gray  matter  as  far  as  the 
pons,  and,  after  the  accessory  has  made  its  exit,  gives  out  fibers  to  the  vagus 
(and  glosso-pharyngeus?),  which  first  ascend  in  a  dorsal  direction,  and  then 
bend  around  to  the  respective  nerve-trunk  (motor  vagus,  etc.,  nucleus). 
Higher  still  it  is  met  as  the  facial  center.  It  must,  therefore,  be  remarked, 
that,  with  the  exceptions  of  the  hypoglossus  and  the  motor  nerves  to  the 
eye,  all  the  motor  fibers  of  the  cranial  nerves  arise  from  a  cellular  column, 
which  lies  in  a  prolongation  upward  of  the  lateral  cells  of  the  ventral  horn. 

Next  one  sees,  in  Fig.  238,  what  has  become  of  the  remainder  of  this 
horn,  and  how  greatly  the  olivary  bodies  have  enlarged.  When  the  lateral 
horn  has  become  separated,  there  appears  where  the  posterior  horn  was 
inserted — in  a  place,  therefore,  which  held  nuclei  of  sensory  nerves  lower 
in  the  cord — a  new,  large  nerve-center,  with  spindle-shaped  cells,  very 
similar  to  those  of  the  dorsal  horn,  the  sensory  center  of  the  vagus  nerve. 
It  lies  in  the  floor  of  the  fourth  ventricle,  median  to  the  ala  cinerea  (Fig. 
236),  and  extends  forward  to  about  the  middle  of  the  white  striffi  acusticae. 


THE    MEDULLA    OBLONGATA. 


375 


Into  this  anterior  part  of  the  center  pass  fibers  of  the  glosso-pharyngeal  nerve, 
The  greater  part  of  this  nerve,  however,  comes  from  its  descending  root  (see 
below).  We  have  learned,  then,  two  nuclei  for  the  vagus:  a  ventral  one, 
which  from  its  position  (in  the  prolongation  of  the  ventral  horn)  and  from 
the  appearance  of  its  cells  (multipolar  with  axis-cylinders  passing  directly 
into  the  nerve)  is  motor;  and  a  dorsal  one,  which,  lying  in  the  prolongation 
of  the  gray  matter  of  the  base  of  the  posterior  horn,  is  also,  by  its  structure, 
characterized  as  sensory.  The  first  of  these  nuclei  is  designated  nucleus 
ambiguus.  The  fibers  to  which  it  gives  origin  pass,  all  of  them,  dorsally, 


trangktm 


X.k 


Fig.  239.— Section  through  the  bulb  at  the  level  of  the  exit  of  the  vagus 
(schematic).  Mot.  Vagus,  etc.,  Kern,  Nucleus  of  motor  vagus,  etc.  Seitenhorn, 
Lateral  horn.  Vorderhornrest,  Remnant  of  anterior  horn.  Seitenstrangkern, 
Nucleus  of  lateral  column.  ScJileifenfasern,  Fibers  of  fillet.  Oliven  Zwisch. 
Schicht,  Interoliyary  layer.  For  other  terms  see  Fig.  238. 

and,  bending  to  form  a  knee,  join  the  much  coarser  fibers  of  the  sensory  root, 
which  pass  out  straight  (Fig.  239).  Besides  these  two  nuclei,  the  vagus  re- 
ceives fibers  from  at  least  two  other  places.  From  the  upper  cervical  cord 
downward  one  may  see  a  fine  column,  which  may  be  traced  upward  to  the 
oblongata,  to  the  place  where  the  last  glosso-pharyngeal  root  emerges.  On 
its  median  side  lies  a  column  of  gelatinous  matter,  in  which  cells  are 


376  ANATOMY    OF   THE    CENTEAL    NERVOUS    SYSTEM. 

sparingly  imbedded.  It  is  called  the  tractus  solitarius,  or  combined  descend- 
ing vagus  glosso-pharyngeal  root.  It  can  be  seen  in  Figs.  234  and  239,  lying 
dorsal  to  the  vagus  roots.  Only  a  small  part  of  the  entering  vagus  roots  turns 
caudally  into  the  funiculus  solitarius,  and  enters,  after  gradually  splitting 
into  end-ramifications,  into  the  neighboring  gray  column. 

This  column  is,  therefore,  the  nucleus  of  the  glosso-pharyngeus  and  a 
portion  of  the  vagus.  S.  Eamon  y  Cajal  has  recently  shown  that  just  at  the 
place  where  the  central  canal  widens  to  form  the  fourth  ventricle  the  two 
terminal  nuclei  of  the  vagus  and  glosso-pharyngeus  nerves  approach  each 
other,  and,  eventually,  at  the  point  where  it  opens,  coalesce  to  one  common 
mass,  the  nucleus  commissuralis.  A  considerable  number  of  the  fibers  of 
the  funiculus  solitarius  cross  over  to  the  other  side  at  this  point. 

The  glosso-pharyngeal  nerve  sends  the  larger  mass  of  its  fibers  to  end  in 
the  gray  matter  of  the  funiculus  solitarius,  while  only  a  relatively  small 
portion  of  them  branch  in  that  of  the  floor  of  the  fourth  ventricle.  Again 
we  have  the  plan  of  the  sensory  nerves:  nerve,  nucleus  of  origin  in  the 
spinal  ganglion;  for  the  nerve-root,  ultimate  center  (sensory  vagus  center); 
and  the  decussated  ascending  central  tract. 

In  the  floor  of  the  fourth  ventricle.,  between  the  vagus  center  and  the  median 
line,  lies  another  small  swelling,  Clarke's  eminentia  teres,  in  which  may  be  found, 
from  the  frontal  end  of  the  hypoglossal  center  on  up  to  near  the  origin  of  the  tri- 
facial,  a  slender  group  of  spindle-shaped  cells:  the  nucleus  funiculi  teretis,  Meynert's 
nucleus  medialis.  Its  importance  is  as  yet  unknown. 

The  hypoglossus  center  consists  of  several  groups  of  ganglion-cells,  all 
bound  together  by  a  fine  net-work.  From  its  large  multipolar  cells  develop 
delicate  twigs,  which,  converging  like  a  brush,  form  a  number  of  small  nerve- 
trunks.  From  this  center  there  develop  fibers,  fibrae  afferentes,  just  as  from 
the  spinal  anterior  horns,  which  cross  over  the  median  line;  they  do  not 
go  far  over  in  the  other  side,  however,  but  extend,  after  passing  the  raphe, 
cerebrally,  and  within  the  pons  are  joined  by  other  fibers  (from  the  facialis 
center).  The  combined  bundle  then  passes  to  the  pes  cerebri.  If  this  course 
be,  perhaps,  a  little  different  from  that  of  the  secondary  (central)  motor 
tracts  in  the  spinal  cord,  still  it  is  materially  the  same:  nerve-root,  nucleus, 
decussating  tract  to  pes. 

A  net-work  which  binds  the  parts  of  the  hypoglossal  center  together  is 
of  especial  interest;  it  occurs  only  in  one  other  center,  the  motor  oculj. 
There  are,  however,  no  other  nerves  whose  fibers  are  called  into  action  so 
simultaneously  and  harmoniously  as  those  of  the  hypoglossus  in  deglutition 
and  those  of  the  oculo-motorius  in  movements  of  the  eyes. 

However,  there  is  demonstrable  in  the  prolongation  of  the  hypoglossal 
net-work,  immediately  under  the  epithelium  of  the  ventricle,  on  both  sides, 
a  meshed  bundle  of  medullated  nerve-fibers  from  which  fibrils  are  given  off 


THE    MEDULLA    OBLOXGATA. 


377 


ventrally  (to  the  nerve-centers).  This  bundle — fasciculus  longitudinalis 
dorsalis  of  Schiitz — lies  in  the  bulb  between  the  vagus  center  and  the 
eminentia  teres.  It  may  be  traced  as  far  upward  as  the  corpora  quadri- 
gemina,  where  it  passes  under  the  fibers  of  the  gray  matter  surrounding  the 
aqueduct  of  Sylvius. 

In  Fig.  240,  a  representation  of  the  hypoglossal  center,  Koch,  to  whom 


x      ^..  • 

Y-  "  "?!&*'        luLciaixn 


Fig.  240. — Frontal  section  through  the  nucleus  of  the  hypoglossal 
nerve.     (After  Koch.) 


we  are  indebted  for  our  knowledge  of  its  net -work,  has  well-shown  its  wealth 
of  fibers  and  cells.  Ventral  from  the  center  are  a  few  cell-groups  (Boiler's 
hypoglossal  center),  from  which,  however,  no  hypoglossal  fibers  arise. 

The  pyramidal  crossing  was  discovered  as  early  as  1710  by  Francois  Petit.     The 
olives  were  first  described  by  Vieussens.     Macroscopic  differences  in  the  development 


378  ANATOMY    OF   THE    CENTRAL    NERVOUS    SYSTEM. 

of  the  oblongata  from  the  cord,  especially  the  surface-changes,  have  been  known 
since  Santorini,,  Reil,  Burdach,  and  Rolando.  The  nuclei  arciformes  and  their  cov- 
ering, fibres  arciformes  anteriores,  were  first  well  described  by  Arnold,  who  regarded 
them  as  "antepons."  The  strise  acusticae  were  discovered  by  Picolhomini.  As  "to 
their  relationship  to  the  auditory  nerve,  there  arose  even  before  the  time  of  micro- 
scopes a  lively  discussion.  Real  light  on  the  construction  of  the  medulla  oblongata 
was  due  to  researches  of  Stilling,  Kolliker,  Meynert,  Schroeder,  Van  der  Kolk,  and 
Deiter.  In  recent  times  attention  has  been  given  to  the  nerve-centers  there  found 
(Gudden,  Roller,  Freud,  Duval,  Koch,  Darkschewitch,  v.  Kolliker,  S.  Ram6n  y  Cajal, 
and  others). 

The  existence  of  this  "glosso-pharyngeal  center"  immediately  in  front 
of  the  vagus  center  is  disputed.  It  is,  in  fact,  difficult  to  find  by  the  usual 
methods  the  small  portion  of  the  nerve  dipping  into  it.  The  employment 
of  the  Golgi  method,  however,  teaches  (Held)  that  the  relations  met  are  as 
just  described.  When  the  glosso-pharyngeal  nerve  is  found  and  has  started 
on  its  course,  one  sees  that  the  small  column  of  gray  matter,  in  which  it 
terminated,  extends  still  farther  anteriorly.  Wallenberg  demonstrated  in  a 
case  of  degeneration  of  the  trigeminus,  in  which  principally  the  sense  of 
taste  suffered,  that  fibers  coming  from  this  anterior  nucleus  enter  the  trigem- 
inus. It  must  therefore  be  conceded  that  this  long,  thin  column  of  gray 
matter  near  the  fasciculus  solitarius  is  the  taste-center,  and  that  fibers  enter 
it  which  run  partly  in  the  trigeminus  and  partly  in  the  glosso-pharyngeus. 
The  supply  of  the  dorsum  lingua?  with  taste-fibers  from  the  glosso- 
pharyngeal  and  chorda  tympani  seems,  accordingly,  to  depend  upon  a  single 
nucleus.  The  pneumogastric  and  glosso-pharyngeal  very  probably  have  an 
additional  descending  root.  It  comes  from  the  cerebellum,  where  we  have 
already  recognized  it  as  the  direct  cerebellar  sensory  tract.  Exactly  which  of 
its  fibers  reach  the  vagus  is,  in  man,  very  difficult  to  demonstrate.  Naturally 
the  sensory  fibers  of  the  nerve  just  mentioned  arise  from  the  cells  of  the 
root-ganglion,  from  which  they  (His)  develop,  the  same  here,  near  the  cere- 
brum, as  do  the  sensory  spinal  nerves.  The  sensory  cells  just  mentioned  are 
their  end-stations.  There  the  fibrils  divide  up  around  cells.  On  the  ventral 
side  of  the  center  one  sees  many  fibers  entering  in  by  curves.  By  the  aid  of 
the  comparative-development  method  it  has  been  demonstrated  that  they 
arise  from  the  lemniscus-layer  of  the  opposite  side.  Therefore  we  have  for 
the  sensory  part  of  the  vagus  (and  the  same  is  true  of  the  glosso-pharyngeus) 
a  decussation  of  its  fibers  soon  after  their  entrance  into  the  cerebro-spinal 
axis. 


CHAPTEK   XXIV. 
THE   MEDULLA   OBLONGATA  AND  THE   TEGMENTUM   OF  THE  PONS. 

HAVING  seen  how,  through  the  rearrangement  of  fibers,  and  the  ap- 
pearance of  new  ganglion-groups  and  the  disappearance  of  the  posterior 
columns,  the  oblongata  is  formed,  there  remain  still  a  number  of  fibrous 
tracts  to  be  followed  upward  from  the  cord.  The  posterior  columns  are  con- 
tinued upward  indirectly  by  the  lemniscus,  and  in  it  also  are  to  be  found 
those  sensory  fibers  of  the  second  order  which  ascend  in  the  antero-lateral 
columns  of  the  cord.  The  pyramidal  tracts  from  both  the  anterior  and 
lateral  columns  lie  now  united,  ventral,  forming  the  thick  pyramid  of  the 
bulb.  The  lateral  cerebellar  tract  retains  its  position  at  the  periphery  as  high 
as  the  olivary  body.  There  its  dorsal  fibrils  begin  to  turn  toward  the  cere- 
bellum, ascending  dorsally.  They  soon  afterward  form  the  nucleus  of  a 
large  bundle,  which  first  appears  here:  the  inferior  cerebellar  peduncle, 
corpus  restiforme.  Its  ventral  portion  occupies  its  original  position  as  far  as 
the  pons,  and  then  turns  backward  toward  the  vermis  superior. 

The  corpus  restiforme  arises  laterally  from  the  upper  end  of  the  pos- 
terior columns,  at  first  because,  as  just  stated,  the  lateral  cerebellar  tract 
there  passes  upward  toward  the  cerebellum.  To  it  pass  also  fibers  from  the 
posterior  columns  of  the  cord,  which,  as  shown  in  Fig.  233  and  Fig.  234 
(above,  to  the  left),  curve  around  the  postero-lateral  periphery  of  the  bulb 
to  join  it,  fibrce  arcuatce  externce  posteriores.  Other  fibers  come  to  them  from 
in  front.  These,  the  fibres  arcuatce  externce  anteriores,  come  apparently  from 
the  lemniscus  between  the  olives, — hence  from  'the  opposite  posterior 
columns, — pass  near  the  median  line  anteriorly  along  the  periphery,  and 
extend  partly  ventrally  to  the  pyramids,  partly  behind  them,  partly  also 
through  them,  around  laterally  to  the  corpus  restiforme.  The  latter  fibers 
have  also  been  called  the  fibrae  arciformes  of  the  pyramids  (Fig.  237). 
Among  them  lies  a  nucleus  of  varying  size,  the  nucleus  arcuatus  (Fig.  241). 
Accordingly,  to  the  corpus  restiforme  there  pass  from  the  spinal  cord  (1)  the 
lateral  cerebellar  tract,  (2)  fibers  from  the  corresponding  posterior  column, 
and  (3)  fibers  probably  from  the  opposite  posterior  column.1 


irrhe  fibers  under  No.  3  receive  their  medullary  sheaths  months  before  those  of 
the  pyramids  and  olives,  probably  at  the  same  time  as  the  posterior  columns. 

(379) 


380 


ANATOMY   OF    THE    CENTRAL   NERVOUS    SYSTEM. 


In  the  period  of  development  represented  in  Fig.  234  only  the  medul- 
lated  fibers  of  the  cord  are  shown.  It  accordingly  shows  well  the  position 
and  extent  of  this  part  of  the  inferior  cerebellar  peduncle.  Fig.  241  also 
shows  the  different  kinds  of  arcif orm  fibers. 

In  the  corpus  restiforme,  however,  besides  the  fibers  from  the  cord,  is 
a  second  and  much  larger  tract,  which,  since  it  is  medullated  much  later 
than  the  former,  must  be  differentiated  from  it.  There  are  fibers  to  the  oppo- 
site olivary  body.  Since  they  come  from  the  cerebellum,  and  cannot  be 
traced  farther  than  the  olive,  they  may  be  known  as  the  tractus  cerebello- 
olivares  .of  the  restiform  body.  By  their  addition  the  inferior  cerebellar 
peduncle  has  now  become  of  considerable  size. 

The  olive,  nucleus  olivaris  inferior,  is  a  hollow  formation  of  the  form 


Fig.  241. — Origin  of  the  spinal  portion  of  the  corpus  restiforme.  The  fibers 
end  mainly  or  entirely  in  the  vermis.  Hinterstrange,  Posterior  columns.  Klein. 
8.  B.,  Lateral  cerebellar  tract. 


of  a  rather  pointed  egg  whose  surface  is  greatly  corrugated.  Toward  the 
median  line  it  has  a  long,  broad  opening — hilum  nuclei  olivaris.  With  the 
much  folded  cross-section  one  is  already  familiar.  When  fresh,  the  olive 
has  a  gray,  transparent  color,  because  it  consists  principally  of  a  thick  mass 
of  neuroglia,  in  which  are  imbedded  much-branched  ganglion-cells.  These 
cells  send  out  a  long  axial  process  (Vincenci),  and  around  them  arborize  the 
terminations  of  another  fiber-system,  from  the  cells  of  Purkinje  (Kolliker). 

Where  the  axis-cylinders  of  the  olivary  cells  go  is  not  yet  known. 
Kolliker  thinks  they  have  relations  to  the  lateral  columns  of  the  cord. 

The  tractus  cerebello-olivares  are  large  bundles  of  fibers,  which  leave 
the  ventral  edge  of  the  restiform  body,  extend  in  graceful  curves  downward 


MEDULLA   OBLONGATA   AND   TEGMENTUM   OF   THE   PONS.  381 

to  the  olive,  and,  then  piercing  the  nucleus  olivaris  from  the  outer  side, 
enter  the  olivary  body.  Thence  the  fibers,  again  collected  in  a  more  compact 
bundle,  leave  by  way  of  the  hilum,  cross  over  the  median  line,  and  terminate 
in  the  opposite  olive.  In  general,  they  pursue  the  same  course  as  the  fibra3 
arcuatae  from  the  fillet,  from  which  they  can  be  distinguished  only  after 
degeneration  (Fig.  242).  If  a  cerebellar  hemisphere  be  destroyed,  they 
dwindle  away  together  with  the  opposite  olive.  Dorsal  to  the  olive  in  the 
region  of  the  substantia  reticularis  are  a  few  strands  of  fibers,  which  are 
connected  with  fibers  from  the  net-work  surrounding  the  ganglion,  and 
extend  upward  in  the  tegmentum  (Bechterew's  central  tract  of  the  tegmentum: 
Stilling's  remnant  of  the  lateral  column). 


Fig.   242. — The   cerebello-olivary   division   of  the   corpus   restiforme.     The   blank 
field  in  the  left  restiform  body  shows  the  position  of  the  spinal  division. 

The  cerebello-olivary  tract  of  the  corpus  restiforme  comes  principally 
from  the  outer  side  of  Stilling's  "fleece."  The  latter  is,  in  turn,  connected 
with  the  superior  peduncle  of  the  cerebellum  (Brachium  conjunctivum)  by 
means  of  the  cerebellar  nucleus  dentatus,  which  it  surrounds.  Consequently 
it  will  be  seen  that  the  olive,  the  opposite  restiform  body,  the  "fleece,"  the 
superior  cerebellar  peduncle,  and  the  red  nucleus  of  the  tegmentum  (also 
of  the  opposite  side)  form  one  conducting  path.  There  is  much  evidence, 
such  as  experiments  on  animals,  which  indicates  that  this  path  is  important 
for  the  maintenance  of  equilibrium  and  of  muscle-tonus.  Only  mammals 
have  large,  distinct  olives  (vide  page  98). 

At  the  level  of  the  pneumogastric  nucleus  in  the  medulla  most  of  the 


382 


ANATOMY    OF    THE    CENTRAL   NERVOUS    SYSTEM. 


fibers  from  the  cord  have  entered  the  restiform  body.  Likewise  it  receives 
there  a  portion  of  the  olivary  tract.  The  inferior  cerebellar  peduncle  lies 
to  the  side  of  the  last  remnant  of  the  posterior  columns,  forming  a  thick 
bundle. 

We  have  here  a  cross-section  typical  of  the  medulla.  After  knowing  the 
single  component  parts  of  this  section  it  will  be  well  to  consider  them  all 
together.  Much  additional  will  appear  thereby  (Fig.  243). 

Ventrally  lie  the  pyramids.  The  long  triangular  bundle  of  fibers,  cut 
across  just  behind  the  pyramids,  is  the  lemniscus  (fillet],  the  decussated  pro- 
longations of  the  posterior  nerve-roots.  The  nuclei  of  the  posterior  columns 


Fig.  243. — Section  through  the  medulla  oblongata.  Aufsteigende  Vagus, 
etc.,  W.,  Ascending  root  of  vagus,  etc.  Vord.  Vag.,  etc.,  W.,  Anterior  root  of 
vagus,  etc.  Hint.  Langsb.,  Posterior  longitudinal  fasciculus.  Aufst.  Trigem. 
Wurz.,  Ascending  root  of  trigerainus.  Seit.  Str.  B.,  Lateral  cerebellar  tract. 
Central  Haul).  B.,  Central  tegmental  tract.  Oliv.  Zwisch.  Schicht,  Interolivary 
layer.  Hint.  Neb.  Olive,  Posterior  accessory  olivary  body.  Innere  Neb.  Olive, 
Inner  accessory  olivary  body. 


lie  posteriorly  and  laterally,  covered  only  by  a  few  nerve-fibers.  Numerous 
fibrae  arcuatse  internae  arise  there  and  crowd  through  the  space  between  the 
posterior  horns  and  the  fillet  to  the  raphe,  and  so  to  the  other  side. 

A  similar  course  is  taken  by  the  cerebello-olivary  fibers.    In  the  figure 


MEDULLA   OBLONGATA   AND    TEGMENTUM   OF   THE   PONS.  383 

the}-  are  represented  by  dots,  but  in  the  adult  the  two  kinds  of  fibrae  arci- 
formes  internse  are  not  to  be  differentiated.  The  examination  of  their 
periods  of  medullation  first  rendered  them  distinct  from  each  other. 

In  the  median  line  all  these  tracts  must  naturally  cross  with  those  from 
the  other  side.  This  line,  with  its  many  crossing  fibers,  is  called  the  raphe. 

The  lemniscus,  or  fillet,  contains  in  this  level,  besides  the  ascending 
paths  of  the  antero-lateral  tract,  also  the  largest  part  of  those  coming  from 
the  nuclei  of  the  posterior  columns.  The  latter  extend  further  forward 
into  the  upper  lemniscus. 

Notice  also  in  the  figure  the  fibrils  passing  from  the  fillet  to  the  oppo- 
site vagus  nucleus;  they  are  analogous  to  the  decussating  fibers  from  the 
antero-lateral  column  to  the  posterior  horn,  the  secondary  vagus  path. 

Dorsal  to  the  lemniscus  we  find  for  the  first  time  again  the  posterior 
longitudinal  fasciculus,  mentioned  in  Chapter  VII.  As  low  as  the  first 
cervical  nerves  its  fibers  are  found  deep  in  the  anterior  column. 

On  either  side,  external  to  the  pyramids,  lie  the  lower  olives.  They  are 
penetrated  by  the  fibra  arcuatas,  which,  as  we  have  learned,  end  in  it  in  so 
far  as  they  come  from  the  cerebellum,  but  pass  through  it  in  so  far  as  they 
come  from  the  nuclei  of  the  posterior  columns. 

Lateral  and  dorsal  to  the  olive  lie  the  inner  and  posterior  accessory  olives, 
nuclei  similarly  constructed  to  the  olives  themselves,  and,  like  them,  are 
penetrated  by  the  arcuate  fibers.  Through  the  first,  the  internal  one,  pass 
the  fibers  from  one  olive  to  the  other,  while  the  posterior  one  is  principally 
pierced  by  the  fibers  from  the  posterior  columns,  as  shown  in  the  figure. 

Dorsal  to  the  olive,  in  the  region  of  the  posterior  accessory  olive,  a  field 
of  white  matter  that  from  now  on  remains  visible  in  the  middle  of  the  teg- 
mentum,  may  be  distinctly  followed  above,  beyond  the  center  of  the 
trigeminus.  The  whole  of  its  fibers  (central  tegmental  path)  connects  prob- 
ably the  olive  with  the  midbrain  (Bechterew). 

The  dorsal  periphery  of  the  section  is  occupied  by  the  nerve-centers. 
Innermost  lies  the  nucleus  of  the  hypoglossus,  whose  fibers,  passing  through 
the  olivary  region,  press  forward  (cf.  Fig.  240).  From  the  raphe  many  fibers 
pass  to  join  it.  External  to  it  lies  the  pneumogastric  nucleus.  A  remnant 
of  the  lateral  cells  of  the  ventral  horn  lies  as  ventral  or  motor  vagus  nucleus 
just  anterior  to  the  posterior  horn.  The  fibers  arising  from  it  form  an  angle 
before  their  exit,  around  which  roots  from  the  sensory  nucleus  arborize. 

The  thin  bundle  of  cross-cut  nerve-fibers,  lying  external  to  the  last- 
mentioned  sensory  nuclei,  is  the  combined  vago-glosso-pharyngeal  root,  with 
its  nucleus  attached. 

External  to  this  common  nucleus  of  the  two  nerves  lie  the  nuclei  of  the 
posterior  columns,  in  front  of  which  is  the  substantia  gelatinosa  from  the 
extremity  of  the  dorsal  horn  of  the  cord.  It  is  bounded  externally  by  a 


384  ANATOMY   OF   THE    CEXTKAL    NERVOUS    SYSTEM. 

thick,  much  separated  bundle  of  medullated  fibers,  which  are  found  in  its 
vicinity  from  the  upper  cervical  cord,  growing  larger  as  they  ascend.  This 
bundle  can  be  traced  as  high  as  the  pons.  There  it  joins  with  the  trigeminal 
fibers  just  issuing.  Eegarding  this  spinal  root  of  the  trigeminus,  cf.  page  364. 

The  territory  between  the  olive  and  the  nuclei  of  the  posterior  columns, 
bounded  externally  by  the  lateral  cerebellar  tract  and  the  ascending  trigem- 
inal root  and  internally  by  the  fillet,  contains,  besides  the  numerous  fibras 
arciformes  internas  a  number  of  short  fibers,  and,  lying  between  these,  scat- 
tered multipolar  nerve-cells. 

The  reticular  appearance  of  the  bundles  of  fibers  in  a  cross-section  of 
the  medulla  justifies  the  appellation  substantia  reticularis.  The  group  of 
cells  have  been  named  nucleus  reticularis  tegmenti  by  Bechterew,  and  it  can 
be  traced  upward  to  near  the  corpora  quadrigemina.  The  cells  and  the 
fibers  are,  as  far  as  we  now  know,  of  the  same  character  as  the  column-cells 
in  the  cord;  by  their  much  divided  axis-cylinders  they  join  different  levels 
of  the  bulb  together.  And  so  the  entire  system  found  in  the  lateral  columns 
of  the  cord  corresponds  closely  with  this  in  the  medulla.  It  is  well,  then, 
to  call  this  characteristic  field  of  the  elongated  cord  the  association-field  of 
the  medulla  oblongata.  It  has  already  been  mentioned  (page  80)  that  upon 
this  wealth  of  association-fibers  probably  is  dependent  the  property  of  the 
oblongata  to  co-ordinate  various  functions,  as  it  does. 

If  one  make  other  sections  of  the  medulla  higher  up,  the  cross-section 
does  not  change  materially  for  about  two  millimeters.  One  sees  that  the 
sensory  nucleus  of  the  pneumogastric,  extending  farther  upward,  continually 
receives  from  the  periphery  root-fibers  in  its  ventral  aspect.  From  the  fas- 
ciculus solitarius  the  fibers  of  the  glosso-pharyngeus  pass  in  small  bundles 
near  the  frontal  end  of  the  vagus  nucleus.  The  restiform  body  alone  here 
increases  greatly  in  circumference.  To  it  pass  in  this  level  the  olivary  fibers 
from  the  cerebellum. 

The  last  sections  before  reaching  the  pons  (Fig.  244)  show  that  the  pos- 
terior columnar  nuclei  have  disappeared,  and  in  their  place  lies  the  thick 
mass  of  fibers  of  the  restiform  body.  To  the  inner  side  of  it  is  a  new  set  of 
fibers  cut  transversely,  the  direct  cerebellar  sensory  tract.  Where  it  began  is 
hard  to  say;  perhaps  it  already  existed  in  the  nuclei  of  the  posterior  columns. 
Besides  this,  in  this  section  we  have  a  descending  acusticus  root.  From  the 
corpus  restiforme  pass  fibers  to  the  inferior  olive,  which  in  this  level  is  much 
smaller  than  below.  The  lemniscus  and  the  tegmentum  occupy  the  same 
positions  as  in  the  last-described  sections.  Three  new  nuclei  have  come  to 
view.  One,  occupying  the  place  where  lower  down  the  motor  fibers  of  the 
vagus  arose  (Fig.  243),  sends  its  fibers  dorsally  and  inward,  where  they  soon 
collect  in  a  bundle  near  the  median  line:  the  nucleus  facialis.  The  second 
of  the  three  new  nuclei  lies  external  to  the  restiform  body.  At  times  we 


MEDULLA    OBLOXGATA    AXD    TEGMEXTUil    OF    THE    POXS. 


385 


may  observe  fibers  entering  it,  which  come  from  the  dorsally-placed  nucleus 
acustici  dorsalis,  which  here  begins  to  be  visible,  while  in  the  following  sec- 
tion may  be  recognized  a  very  large  center,  the  ventral — formerly  anterior — 
nucleus  of  the  acusticus.  One  can  see  already  in  this  section  how  it  is  placed 
between  the  cerebellum  and  the  restiform  body.  A  protuberance  lateral  to 
it,  on  the  surface  of  the  medulla  oblongata,  is  called  the  tuberculum  acusti- 
cum. 

Passing  upward  again,  we  come  to  the  place  where  the  first  fibers  of  the 


Fig.  244. — The  relations  of  the  oblongata  to  the  inferior  edge  of  the  pons. 
Dir.  sens.  Cereb.  B.,  Direct  sensory  cerebellar  tract.  Centr.  H.  B.,  Central  teg- 
mental  tract. 


pons  Varolii  are  ventrally  superimposed  on  the  pyramids,  coming,  as  they 
do,  from  the  cerebellum. 

All  the  following  sections,  therefore,  will  show  in  the  ventral  portion 
the  greatly  intertwined  crus  portion  of  the  pons.  It  changes  relatively  little 
up  as  far  as  the  levels  described  in  Chapter  XX. 

Much  more  complicated  than  the  crus  portion  is  the  tegmental  part  of 
the  pons.  Here  begins  a  locality  of  the  brain  in  which  in  a  relatively  very 
narrow  space  are  crowded  together  important  structures,  the  region  into 
which  passes  the  acusticus,  and  from  which  arise  the  facialis  and  abducens. 


386 


ANATOMY    OF    THE    CENTRAL    NERVOUS    SYSTEM. 


The  eighth  cranial  nerve  consists  of  two  nerves,  which  have,  as  is  well- 
known,  different  functions.  It  has  been  proposed,  in  view  of  this  fact,  to 
separate  the  two  bundles — nervus  cochleae  and  nervus  vestibuli — and  to 
consider  only  the  first  as  the  auditory  nerve,  regarding  the  other  as  the 
tonus  nerve. 

The  cochlear  nerve  originates  in  cells  of  the  spiral  ganglion  of  the 
cochlea.  These  cells  send  out  peripherally  a  delicate  branch,  which  rapidly 


Fig.  245. — The  most  important  features  in  the  region  of  the  origin 
of  the  acoustic  nerve. 


splits  up  between  the  auditory  cells  (Fig.  16,  &),  while  centrally,  analogous  to 
the  posterior  root  from  the  spinal  ganglion-ceils  to  the  cord,  the  auditory 
nerve-root  passes:  the  nervus  cochleae. 

In  the  section  (Fig.  245)  one  sees  fyow  this  bundle,  earlier  known  as  the 
"radix  posterior,"  enters  with  delicate  fibers  into  the  above-mentioned 
nucleus  acustici  ventralis.  It  divides  into  a  delicate  arborization  around  the 
large  cells  of  this  nucleus.  To  a  less  extent  it  passes  into  a  relatively  small 


MEDULLA    OBLOXGATA    AND    TEGMEXTUM    OF   THE    POXS. 


387 


ganglion  in  man,  in  animals  often  very  large,  situated  between  the  cere- 
bellum and  pons,  dorso-lateral  from  the  cochlear  nucleus.  This  is  the 
tuberculum  acusticum.  This  portion  also  arborizes  around  cells.  And  so  the 
primary  neuron  of  the  cochlearis  terminates  in-  these  two  places. 

From  the  two  primary  termini  arises  a  new  fiber-tract,  which  in  its 
secondary  and  tertiary  prolongation  reaches  eventually  the  lateral  lemniscus, 
or,  rather,  forms  this  lemniscus. 

1.  The  cells  of  the  nucleus  ventralis  send  out  their  axis-cylinders 
toward  the  median  line,  where  they  are  seen  to  leave  the  center  as  a  strong 
bundle.  This  tract  is  called  the  corpus  trapezoideum.  It  lies  directly  dorsal 
to  the  pontile  fibers,  and  in  animals,  because  their  pons  is  shorter  than  in 
man,  is  visible  free  on  the  base  of  the  brain  (vide  Fig.  246). 

Within  the  trapezoid  body  are  scattered  large  cells,  nucleus  trapezoideus 


Fig.  246. — Medulla  oblongata  and  pons  of  a  monkey,  demonstrating  the  corpus 
trapezoideum  or  trapezium,  ct.    a,  Pyramids. 


(Kolliker),  whose  axis-cylinders  take  the  same  direction  as  the  thick  trape- 
zoid fibers  of  the  cochlear  nucleus. 

The  entire,  rather  important  mass  of  fibers  extends  to  a  small  group  of 
ganglion-cells,  the  superior  olivary  nucleus,  and  as  much  to  the  same  side  as 
by  decussation  to  the  opposite  side  (Fig.  245).  And  here,  seemingly,  the 
secondary  auditory  neuron  ends.  To  the  upper  olive  come  the  fibers  of  the 
lateral  fillet,  a  dense  arborization.  In  this  way  connection  between  the 
acusticus  and  the  posterior,  perhaps  also  the  anterior,  corpora  quadrigemina 
is  established. 

Degeneration  changes  (Bumm,  Baginski)  make  it  appear  that  not  only 
the  fillet-fibers  descending  here  give  off  a  great  many  collaterals  around  the  • 
upper  olivary  nucleus,  but  also  that  from  this  nucleus  itself,  from  the 
nucleus  trapezoideus,  and  from  the  striae  acustica?,  presently  to  be  described, 
pass  numerous  tracts  of  fibers  into  the  fillet,  and  extend  upward  with  it  to 


388  ANATOMY    OF   THE    CENTRAL    NEKVOUS    SYSTEM. 

the  posterior  corpora  quadrigemina.  To  these  would  be  associated,  also, 
fibers  arising  in  the  nuclei  situated  in  the  lateral  fillet  just  back  of  the  cor- 
pora quadrigemina  (vide  Fig.  206,  I,  outer  side).  The  lateral  fillet,  therefore, 
contains  principally  numerous  neurons  from  the  tertiary  acusticus  end- 
stations. 

2.  Kegarding  the  fossa  rhomboidalis  from'  above,  one's  attention  is 
drawn  to  several  thick  strands  which,  emerging  out  of  the  raphe,  extend 
laterally  and  lose  themselves  in  the  tissues  close  up  to  the  cerebellum. 
They  do  not  all  arise  near  together;  it  occurs  rather  often  that  one  or 
another  of  these  bundles  arises  much  farther  forward  in  the  floor  of  the 
sinus,  and  extends  backward  in  relatively  long  reaches,  before  it  joins  the 
other  bundles  at  the  level  of  the  acusticus.  This  striation  is  called  the  strics 
acusticce;  to  the  long,  occasionally  aberrant  bundle  in  front  Bergman  has 
applied  the  name  conductor  sonorus. 

While  the  first  division  of  the  cochlearis  is  connected  with  the  fillet 
through  the  medium  of  the  corpus  trapezoideum  and  the  upper  olive,  it  is 
different  with  the  part  ending  in  the  tubercle.  This  sends  its  strands  direct 
into  the  secondary  acusticus  tract,  in  the  opposite  fillet,  and  these  fibers  are, 
in  fact,  the  striaa  acusticae. 

Following  their  course  more  topographically,  the  striae  arise  out  of  the 
tuberculum  acusticum,  situated  between  the  pons  and  the  cerebellum,  and  to 
a  smaller  extent  from  the  large  cochlear  nucleus  (nucleus  ventralis  in  the 
figure),  and  then  pass  laterally  around  the  corpus  restiforme,  ju^t  under  the 
ependyma  of  the  ventricle  toward  the  median  line.  Near  the  raphe  they  dip 
down  deeper,  and,  while  in  the  raphe  itself,  they  turn  anteriorly  and  cross 
over  to  the  opposite  side,  where  they  join  the  lateral  fillet,  considerably 
augmenting  its  volume. 

Monakow  saw  atrophy  of  the  striae  after  destruction  of  the  opposite  lateral 
fillet  high  up  near  the  corpora  quadrigemina.  Bumm  and  Baginsky  observed  them 
degenerate  toward  the  corpora  quadrigemina  after  destruction  of  the  cochlea.  The 
lateral  fillet  must,  therefore,  contain  fibers  running  in  opposite  directions. 

It  will  be  seen  that  the  point  of  greatest  importance  in  this  complicated 
arrangement  is  that  the  nervus  cochlearis,  after  once  terminating  in  the 
nucleus  cochlearis  and  the  tuberculum  acusticum,  has  a  higher  tract  going 
to  the  posterior  corpora  quadrigemina.  It  runs  by  way  of  the  lateral  lem- 
niscus.  Still,  only  a  portion  of  its  fibers  enters  the  lemniscus  directly 
through  the  striae;  a  second  very  considerable  portion  passes  first  to  the 
oliva  superior,  traversing  the  trapezoid  body,  and  thence  arises  the  tract, 
which  enters  the  fillet  and  there  joins  the  fibers  from  the  striae  acusticae. 

The  upper  olives,  interposed  as  they  are  in  the  central  auditory  nerve- 
fibers,  must  be  centers  of  importance.  Their  constant  occurrence  through 


MEDULLA    OBLOXGATA   AND   TEGMENTUM   OF   THE    PONS. 


389 


the  entire  list  of  mammals,  their  frequently  large  development,  and,  above 
all,  the  wealth  of  fibers  entering  into  relation  with  them  are  evidence  of  this. 
Among  these  are  fibers  from  the  cerebellum,  still  but  little  understood,  and  a 


large  strand  from  the  center  of  the  nervus  abducens,  well  represented  in 
Fig.  248.  Since  in  this  center  of  the  sixth  nerve,  however,  fibers  end  which 
pass  through  the  fasciculus  longitudinalis  posterior  to  the  centers  of  the 


390 


ANATOMY    OF    THE    CENTRAL    NERVOUS    SYSTEM. 


other  motor  nerves  of  the  eye  and  to  the  thalamus,  there  is  here  apparently  a 
well  organized,  synergetic  apparatus,  well  deserving  further  experimental 
research. 

Much  less  is  known  of  the  other  branch  of  the  eighth  nerve,  the  nervus 
vestibularis.  It  arises  from  ganglion-cells  lying  in  the  labyrinth  and  also  in 
the  nerve-trunk  itself.  These  cells  send  a  small  branch  into  the  sensory 


Fig.  248. — Section  through  the  region  of  the  origin  of  the  abducens.     Origin 
of  the  nervus  vestibularis. 


epithelium  in  the  ampulla?,  where  it  arborizes  in  extremely  delicate  filaments 
around  the  base  of  the  epithelium,  and  a  second  branch  into  the  nerve. 

Of  the  two  fasciculi  converging  to  the  acusticus,  the  anterior  one  is  the 
vestibular.  It  extends,  median  to  the  restiform  body  and  the  ascending 
trigeminal  root,  dorsally  through  the  medulla  to  the  gray  matter  in  the 
floor  of  the  fourth  ventricle.  A  portion  of  its  fibers  ends  there  with  terminal 
branches  in  the  dorsal  nucleus.  These  fibers,  just  like  the  sensory  spina] 


MEDULLA   OBLOXGATA    AXD   TEGMENTUM   OF   THE    PONS.  391 

roots  entering  the  posterior  columns,  before  splitting  up  in  the  gray  matter, 
emit  fibers  posteriorly,  the  descending  root  of  the  acusticus  (Roller).  A  part 
of  the  fibers  of  the  nervus  vestibularis  does  not  end  in  the  dorsal  nucleus, 
but  is  distributed  to  nuclei,  as  yet  insufficiently  known,  lying  between  the 
vermis  cerebelli  and  the  medulla  oblongata. 

The  nucleus  dorsalis,  nucleus  nervi  vestibularis,  is  an  elongated  body, 
prismatic  on  cross-section,  which  appears  in  sections  lower  down,  where  the 
anterior  vagus  root  is  given  off  (vide  Fig.  244). 

Of  the  other  end-stations,  at  present  the  most  certain  is  Bechterew's 
nucleus,  which  lies  in  the  lateral  wall  of  the  ventricle  median  to  the  fibers  of 
the  corpus  restiforme  rising  to  the  cerebellum,  and  which  extends  in  scat- 
tered gray  clumps  upward  to  near  the  cerebellum. 

The  vestibular  nerve  has,  too,  a  large  number  of  anatomical  relations 
with  other  regions  of  the  brain.  The  nucleus  dorsalis  is  connected  with  the 
superior  olive  by  one  tract,  and  with  the  cerebellum  by  another  issuing 
laterally.  About  the  cerebellar  relations  of  the  vestibular  fibers,  which 
extend  farther  upward  above  this  nucleus,  we  know,  as  yet,  nothing  certain. 

The  origins  of  the  acusticus,  which  remained  long  obscure,  have  been  studied 
in  late  years  by  different  investigators,  who  did  not  all  arrive  at  the  same  con- 
clusions as  those  given  here,  the  results  of  personal  examinations.  Freud  and  the 
author,  working  on  human  embryos,  came  to  practically  the  same  conclusions; 
Bechterew  and  Flechsig  contend  that  the  anterior  root  does  not  come  from  the  dorsal 
nucleus,  but  rather  from  cells  in  the  neighborhood  of  Deiter's  nucleus.  The  origin 
of  the  posterior  root  in  the  ventral  nucleus  is  admitted  by  all.  This  nucleus  becomes 
atrophic  after  pulling  away  the  auditory  nerve  (Forel,  Onufrowics,  Baginsky).  We 
are  indebted  to  Kolliker  for  a  very  exact  examination  of  the  entire  apparatus. 

Retzius  and  Gehuchten  have  studied  the  end-branches  in  the  ear,  so  important 
to  our  understanding  of  the  acusticus,  and  the  relations  of  the  ganglion-cells  there 
found.  For  the  finer  details  as  to  the  arborization  in  the  single  nuclei,  the  directions 
of  Held  have  been  followed;  his  examination,  made  prinicpally  by  the  use  of  Golgi's 
method,  based  on  earlier  studies,  has  recently  been  corroborated  by  Bumm  in  ex- 
perimental work. 

Lateral  from  the  nucleus  acustici  dorsalis  lies  the  field  of  the  direct 
cerebellar  sensory  tract.  From  it  probably  pass  fibers  to  the  acusticus.  It 
passes  to  the  cerebellum,  occupying  at  this  level  the  inner  division  of  the 
restiform  body.  In  its  substance  at  this  point  lies  a  nucleus,  of  as  yet  un- 
known significance,  formerly  termed  the  external  auditory  nucleus.  It 
atrophies  when  the  corresponding  half  of  the  cervical  cord  is  cut  through 
(Monakow).  Its  connection  with  the  auditory  nerve  is  not  yet  established. 
For  the  present  it  is,  perhaps,  better  to  call  it  Deiter's  nucleus,  after  its  dis- 
coverer, who  has  rendered  such  distinguished  service  in  bulbar  anatomy. 

In  those  sections  which  contain  the  ventral  acusticus  center  the  nucleus 
of  the  facial  nerve  is  visible  (Fig.  248).  It  consists  of  a  long  row  of  cells 


392  ANATOMY   OF    THE    CENTRAL    NERVOUS    SYSTEM. 

arranged  in  groups.  From  these  arise  continually  fibers,  extending  dorsally. 
They  are  gradually  gathered  to  form  a  good-sized  bundle,  which,  arrived 
within  the  floor  of  the  ventricle,  suddenly  turns  forward,  and  then  as  sharply 
bends  around  to  the  external  side  of  the  bulb.  The  root  of  the  facialis 
accordingly  makes  a  double  knee  (vide  Figs.  245,  248,  249,  and  250).  In  this 
knee  is  deposited  the  nucleus  of  the  abducens  nerve. 

To  the  trunk  of  the  root  of  the  facial  nerve  pass  fibers  from  the  ascending  root 
of  the  trigeminal.  This  is,  perhaps,  important,  because  we 'know  that  from  this  por- 
tion of  the  trigeminus  are  derived  the  sensory  fibers  for  the  face. 

At  precisely  the  place  where  the  facialis  makes  its  exit  from  the  brain 
there  enters  in  a  thin,  delicate  nerve-trunk,  that  has  accompanied  the  pe- 
ripheral course  of  the  facial.  It  is  the  portio  intermedia  Wrisbergi. 

Duval  first  discovered  that  it  arises  from  the  superior  end  of  the  glosso-pharyn- 
geal  nucleus  (Kolliker  says  from  the  nucleus  of  the  fasciculus  solitarius),  and  P. 


Fig.  249. — Schema  of  the  central  path  of  the  nervus  facialis  and  nervus  abducens. 

Martin  and  His  corroborate  this.     The  latter  were  able  to  demonstrate  in  the  em- 
bryo that  fibers  grow  into  the  brain  from  the  ganglion  geniculi  nervi  facialis. 

The  ganglion  geniculi — besides  being  principally  a  sympathetic  gan- 
glion (Lenhossek) — is  then  the  nucleus  of  origin  of  the  portio  intermedia, 
while  the  anterior  portion  of  the  fasciculus  solitarius  is  its  central  nucleus. 

The  roots  of  the  abducens  arrive  by  several  extended  bundles,  which  pass 
through  the  tegmentum  and  the  pons,  at  the  base  of  the  pons  externally. 
On  the  median  side  the  nucleus  is  connected  with  the  posterior  longitudinal 
bundle.  It  is  claimed,  though  not  well  proved,  that  these  fibers  higher  up 
enter  the  opposite  motor-oculi  nerve.  Without  dotibt,  however,  there  is  a 
remarkable  connection  between  the  abducens  nucleus  and  the  superior  olive. 
This  connecting  tract,  which  is  shown  in  Fig  248  parallel  to  the  root  of  the 
facial,  must  place  the  acusticus  in  connection  with  the  motor  nerves  to  the 
eyes,  and  is,  perhaps,  of  importance  for  the  maintenance  of  position  in  space. 


MEDULLA    OBLOXGATA   AXD    TEGMENTUM    OF   THE    PONS.  393 

Before  ascending  farther  it  will  be  well  again  to  consider  the  above- 
mentioned,  but  not  particularly  described,  tegmental  region,  and  to  learn  its 
position  and  relations  in  this  level.  One  feature,  the  nucleus  reticularis  teg- 
menti,  which  lies  with  the  fibers  of  the  substantia  reticularis  scattered  over 
the  region  between  the  raphe  and  the  facialis  root,  is  not  included  in  the 
illustrations,  in  order  to  preserve  their  clearness.  It  is  to  be  found,  how- 
ever, in  all  the  sections  thus  far  considered. 

The  accompanying  Fig.  250  follows  the  sections  just  described,  and  is 
to  demonstrate  how  the  facialis  turns  about  after  coursing  a  short  distance 
ventrally,  and  how  the  direct  sensory  cerebellar  tract  now  passes  upward 
into  the  cerebellum. 


Fig.  250. — Section  at  the  place  where  the  inner  division  of  the  corpus 
restiforme  merges  into  the  cerebellum. 


In  the  cerebellum  are  to  be  seen  in  this  level  the  peduncles  coining 
from  in  front. 

When  the  acusticus,  the  facialis,  and  the  abducens  leave  the  tegmentum, 
the  cross-section  appears  naturally  much  more  simple. 

We  come  to  the  place  of  entrance  of  the  nervus  trigeminus,  and  first  the 
motor  nucleus  of  the  trigeminal  appears  in  the  continuation  of  the  nucleus 
facialis,  though  somewhat  more  dorsal.  From  it  arises,  also  by  a  slight 
"knee,"  the  motor  root,  the  portio  minor,  supplying  the  muscles  of  mastica- 
tion. Probably  there  pass  with  it  fibers  coming  from  the  opposite  motor 
nucleus,  which  cross  over  the  raphe. 

With  the  motor  trigeminus,  course,  also,  fibers  from  the  pons,  which 


394  ANATOMY    OP    THE    CENTRAL    NERVOUS    SYSTEM. 

arise,  not  in  the  motor  nucleus,  but  high  up  in  the  quadrigeminal  region, 
where  laterally  from  the  aquseductus  Sylvii  (in  Fig.  199  above  to  the  left) 
scattered  ganglion-cells  give  rise  to  the  radix  mesencephalica  nervi  trigemini. 
These  cells  continue  downward  always  in  the  lateral  wall  of  the  canal,  and 
one  can  detect  a  more  considerable  collection  of  them  through  the  thin 
ventricular  ependyma,  forming  a  dark  bunch  on  either  side  at  the  beginning 
of  the  fourth  ventricle.  It  is  there  called  the  locus  cceruleus. 

The  nucleus  of  the  motor  nerves  of  mastication  is  made  up  much  -the  same  as 
the  other  motor  centers  in  the  spinal  cord.  Lately,  however,  S.  Ramon  y  Cajal  has 
discovered  in  it  a  peculiar  arrangement.  The  root  from  the  midbrain,  coming  from 
the  large,  swelled  cells  around  the  aqueduct,  gives  off  to  the  large  motor  main 
nucleus  a  great  number  of  extremely  fine  collaterals.  Each  cell  there  is  surrounded 
by  a  very  thick  net  of  such  fibrils.  The  discoverer  of  this  remarkable  arrangement 
is  of  the  opinion  that  it  is  possible  by  these  collaterals  for  a  relatively  weak  impulse, 
originating  in  the  higher  nucleus,  to  be  transformed  in  the  main,  or  lower,  nucleus 
to  a  powerful  stimulus.  The  large  motor  cells  might  be,  as  it  were,  laden,  and  at 
times  simultaneously  discharged,  bringing  about  the  strength  and  the  co-ordination  of 
the  act  of  mastication. 

The  main  portion  of  the  nervus  trigeminus,  the  sensory,  arises,  without 
doubt,  from  the  cells  of  the  Gasserian  ganglion,  whose  peripherally  directed 
branch  forms  the  nerve,  just  as  in  the  spinal  ganglion-cells,  while  a  thick 
"root"  running  centrally  enters  the  pons.  It  penetrates  this  and  disappears, 
to  a  small  extent,  in  the  nucleus  there  situated  (sensory  trigeminal  nucleus). 

As  the  fibers  enter  the  nucleus  the  majority  of  them  split  into  a 
delicate  ascending  branch  and  a  descending  one.  The  former  terminates 
soon  in  the  part  of  the  nucleus  above  where  the  fiber  enters,  forming 
a  delicate  arborization;  the  latter  terminates  more  gradually,  giving  off 
large  numbers  of  collaterals,  and  the  nucleus  in  which  this  occurs,  the  caudal 
continuation  of  the  nucleus  just  mentioned,  is  unusually  long  and  extends, 
as  the  nucleus  terminalis  nervi  trigemini,  as  far  downward  as  the  cervical 
cord.  Throughout  its  extent  it  is  accompanied  by  the  mass  of  trigeminal 
fibers,  naturally  growing  continually  thinner.  Their  cross-section  is  seen 
in  all  the  series  from  the  cervical  cord  up,  as  a  slender,  crescentic  bundle. 
This  tractus  bulbo-spinalis  nervi  trigemini  is  in  close  proximity  to  the  long, 
vitreous  column  of  the  nucleus,  as  far  as  the  posterior  horn  of  the  cervical 
cord,  and  there  finally  vanishes. 

In  Fig.  251  is  shown  a  schematic  representation  of  the  tracts  of  the 
separate  trigeminal  roots.  Many  of  the  details  included  are  after  prepara- 
tions by  Eamon  y  Cajal. 

From  the  long  bulbar  nucleus  of  the  sensory  portion  of  the  trigeminus 
arises  the  secondary  trigeminal  tract.  Several  years  ago,  based  on  investiga- 
tions in  comparative  anatomy,  it  was  demonstrated  that  there  is  a  decus- 


MEDULLA    OBLOXGATA   AND   TEGMEXTUM    OF   THE    POXS.  395 


396 


ANATOMY    OF    THE    CENTRAL    NERVOUS    SYSTEM. 


sating  path  reaching  upward  from  the  bulbar  trigeminal  nucleus.  The 
fibers,  which  throughout  its  extent  leave  this  nucleus  and  cross  over  the 
median  line,  have  since  then  been  frequently  seen;  but  only  lately  Wallen- 
berg succeeded  in  making  a  section  of  them  and  demonstrating  where  the 
central  path  of  the  trigeminus  lies  in  the  brain  and  where  it  ends.  His 
examinations  were  made  on  rabbits.  It  was  seen  that  the  degenerated  path, 


\iffi  I  /    //;^^^?§^v     s2c&-i$& 

f*:,^~;-%fc 

.,    Wf       .«  ^)*   W) 

"*•  M 


Fig.  252. — Section  at  the  place  where  the  ascending  trigeminal  root  turns 
around  externally.  Trigeminal  roots.  Dir.  sens.  Cerebellarbahn,  Direct  sensory 
cerebellar  tract.  Centr.  V.  Bahn,  Central  tract  of  fifth  nerve.  Centr.  H.  B., 
Central  tegmental  tract. 


appearing  after  separation  of  the  bulbar  nucleus,  was  within  the  great  asso- 
ciation-field in  the  lower  bulbar  sections,  close  under  the  hypoglossal 
nucleus,  on  the  opposite  side  to  the  lesion,  and  was  connected  with  it  by 
long,  curved  fibers.  Higher  up  one  finds  it  gradually  taking  a  more  lateral 


MEDULLA   OBLONGATA   AND   TEGMENTUM   OF   THE    PONS.  397 

position  and  somewhat  ventral  to  the  posterior  longitudinal  bundle.  In 
man  one  finds  in  the  same  place  as  in  rabbits  a  large  number  of  transversely- 
divided  fibers  (Fig.  201,  a).  But  the  demonstration  by  the  degeneration- 
method  is  wanting  to  show  their  connection  with  the  trigeminus.  Compare, 
also,  the  area  in  Fig.  199,  marked  "aus  Thalamus."  In  the  midbrain  one 
finds  the  central  trigeminal  path  lateral  to  the  descending  fibers  of  the  pos- 
terior commissure,  and  they  may  be  finally  traced,  according  to  Wallenberg, 
into  the  ventral  nucleus  of  the  thalamus,  where  it  approaches  the  upper 
fillet,  or  its  end-station. 

S.  Eamon  y  Cajal  discovered  the  same  path  independently  of  Wallen- 
berg, at  least  in  its  place  of  origin,  and  has  given  us  an  exhaustive  descrip- 
tion of  the  structure  of  its  bulbar  nucleus.  This  contains  a  multitude  of 
conspicuous  multipolar  cells.  Around  fchese  peripherally  arborize  the  fibers 
of  the  trigeminal  root,  and  from  these  cells  arise  the  axis-cylinders  of  the 
central  tract.  Of  these  the  majority  pass  over  to  the  other  side,  as  stated 
above,  and  there  extend  upward  as  the  most  dorsal  bundle  of  the  substantia 
reticularis,  a  smaller  number,  however,  according  to  E.  y  Cajal,  remaining 
on  the  same  side.  There  is  here  a  contradiction  to  the  results  furnished  by 
the  degeneration-method  of  experiment. 

From  the  central  trigeminal  path  issue  numerous  collaterals  to  the  facial 
nucleus,  furnishing  the  sensory-motor  reflex-arc  for  the  face.  Section  of 
the  trigeminus  is,  therefore,  accompanied  by  not  inconsiderable  motor  dis- 
turbances in  the  face,  due  to  the  loss  of  the  sensory  control. 

The  main  branch  of  the  fifth,  where  it  enters  the  pons  near  the  motor 
nucleus,  is  called  the  portio  major.  In  this  portio  major  trigemini  are  in- 
cluded also  the  fibers  of  the  direct  sensory  tract  descending  from  the  cere- 
bellum. 

From  the  exit  of  the  fifth  up  to  the  exit  of  the  trochlearis  the  pontile 
tegmentum  presents  a  relatively  more  simple  structure  than  that  we  have 
learned  lower  down.  In  the  last  section  demonstrated  the  corpus  resti- 
forme  began  to  separate  from  the  great  mass  of  the  cerebellum.  It  leaves  it 
entirely  now  and  approaches  on  either  side  laterally  to  the  tegmentum,  thus 
forming  its  outermost  boundary  in  the  dorsal  area. 

The  lateral  boundary  further  ventral,  just  over  the  pontile  fibers,  is 
formed  by  the  lemniscus,  and  more  especially  by  that  part  of  it  coming 
from  the  cell-bodies  of  the  sensory  nerves,  is  distinguished  as  the  lateral  or 
inferior  lemniscus,  as  differentiated  from  the  median  portion,  which  comes 
mostly  from  the  nuclei  of  the  posterior  columns  of  the  cord.  The  frontal 
portion  of  the  tegmentum  is  imbedded  in  the  lemniscus  fibers,  as  in  a  trough 
(Fig.  253).  The  horizontal  part  of  this  trough  belongs  ma.inly  to  the  median 
lemniscus.  It  separates  in  wide  extent  the  tegmental  fibers  from  the  al- 
ready numerous  fibers  of  the  crura  in  the  region  of  the  pons.  And  so  arises 


398 


ANATOMY    OF   THE    CENTRAL    NERVOUS    SYSTEM. 


again  the  picture  of  the  quadrigeminal  region,  already  considered,  and  it 
remains  so  on  upward. 

The  median  fillet  extends  at  first  in  the  lemniscal  layer  upward,  and 
finally  arrives,  as  has  been  described,  frontal  to  the  corpora  quadrigemina  in 
the  area  ventral  to  the  thalamus,,  where  it  ends  in  the  ventral  nucleus  of  the 
thalamus. 

The  lateral  fillet — which  contains  besides  the  acusticus-fibers,  all  the 
fibers  from  the  deep  bulbar  nuclei  of  the  sensory  nerves  to  the  roof  of  the 


Fig.  253. — Section  through  the  upper  region  of  the  pons,  in  a  nine-months' 
fetus.  Sindearm,  Anterior  peduncle  of  cerebellum.  Hint.  Langsbiindel,  Post, 
longitudinal  fasciculus.  Schleife,  Fillet.  Briicke,  Pons. 


mesencephalon — in  the  levels  above  the  exit  of  the  trigeminal  turns  out  of 
the  lemniscus  layer  dorsally,  and  extends  on  the  external  side  of  the  pontile 
tegmentum,  diagonally  upward  to  the  corpora  quadrigemina,  under  which 
it  disappears.  Its  well-marked  band  is  easily  recognizable  laterally  in  the 
uninjured  cerebral  axis.  Where  the  fillet  turns  dorsally  are  found  its  gan- 
glion-cells imbedded  (lateral  lemniscal  nucleus,  Obersteiner).  This  group 
may  be  traced  anteriorly  as  far  as  the  superior  nucleus  of  the  lemniscus? 
situated  on  the  outer  edge  of  the  substantia  nigra. 


MEDULLA    OBLONGATA   AND   TEGMENTUM    OF   THE    POXS.  399 

Flechsig  and  Hosel  have  proved  that  the  median  fillet  ends  in  the  nuclei  of  the 
posterior  columns  of  the  cord.  They  consider  the  whole  bundle  direct  from  the 
cerebrum  as  the  cortical  fillet.  It  has  already  been  stated  that  the  cerebral  tract, 
here  concerned,  ends  in  the  ventral,  thalamic  nucleus,  and  that  there  the  median,  or 
superior,  fillet  arises. 

So  we  have  lemniscal  fibers  to  all  the  sensory  bulbar  nuclei.  The  lem- 
niscus  contains,  therefore,  the  secondary  sensory  fibers,  and  conducts  them  up- 
ward to  the  mesencephalon  and  the  thalamus.  Monakow  succeeded  in  demon- 
strating the  experimental  proof  of  this  at  the  same  time  that  the  author 
called  attention  to  it  from  comparative  anatomy.  In  experimental  pro- 
duction of  degeneration  the  fillet  may,  indeed,  be  separated  into  its  various 
bundles  for  the  different  nerves,  trigeminus,  acusticus,  etc. 

In  the  same  horizontal  level  as  the  fillet,  dorsal  to  the  pons,  one  finds, 
near  the  median  line,  another  bundle  of  thick  fibers.  It  comes  from  the 
pyramidal  region  of  the  crura.  It  has  already  been  shown  how  it  separates 
there,  and,  passing  around  the  entire  crus  internally,  reaches  the  median 
side  of  the  fillet.  Spitzka,  from  comparative  anatomy,  has  made  it  seem 
probable  that  this  bundle  contains  the  central  paths  of  the  motor  cranial 
nerves.  As  a  matter  of  fact,  one  can  convince  himself  that  from  it  fibers 
ascend  continually  toward  the  raphe,  and  can  see  on  the  dorsal  end  of  the 
raphe  fibers  crossing  over  the  median  line  to  the  nuclei,  at  least  to  that  of  the 
hypoglossus. 

We  arrive  now  gradually  in  the  region  of  the  pons,  where  the  roof  of 
the  metencephalon  is  no  longer  formed  by  the  cerebellum,  but  rather  by 
the  velum  medullare  anticum.  Here  the  fourth  ventricle  begins  to  narrow 
down  into  the  aquseductus  Sylvii. 

The  single  component  parts  of  the  tegmentum  in  this  level  appear  dis- 
tinctly in  the  accompanying,  not  schematic,  transverse  section  through  the 
uppermost  portion  of  the  pons  in  a  fetus  of  nine  months.  In  the  crus  at  this 
time  there  is  but  a  small  bundle  of  medullated  fibers.  In  the  tegmentum, 
however,  the  lemniscus,  the  brachium  (superior  cerebellar  peduncle),  .the 
posterior  longitudinal  fasciculus,  and  many  fibers  of  the  substantia  reticu- 
laris  are  completely  developed.  The  brachium  passes  directly  into  the 
velum  medullare  anticum,  on  which  rests  the  anterior  part  of  the  lingula. 
Below,  above  the  lemniscus,  can  be  seen  the  hindmost  fibers  of  the  brachia 
crossing. 

The  descending  trigeminal  root  lies  on  either  side  of  the  aqueduct  as  a 
thin  bundle  of  fibers.  Median  to  it,  underneath  the  floor  of  the  fourth  ven- 
tricle or  the  anterior  portion  of  the  sinus  rhomboidalis,  must  be  imagined 
the  cells  of  the  locus  creruleus,  which  were  not  distinct  in  the  preparation 
copied.  The  substantia  reticularis  here  consists  principally  of  longitudinal 
fibers,  which  can  be  followed  upward  only  as  high  as  the  anterior  quadri- 


400  ANATOMY   OF    THE    CENTEAL   NEEVOTJS    SYSTEM. 

geminal  bodies.  Near  the  middle  line  on  either  side  lies  the  fasciculus 
longitudinalis  posterior.  From  this  point  on  to  the  quadrigeminal  region 
there  are  no  important  changes  in  the  appearance  of. the  cross-section  of  the 
tegmentum.  The  fillet  extends  dorsally  on  the  outer  side.  The  brachia 
retreat  toward  each  other,  and  finally  decussate  higher  up. 

The  fibers  of  the  crus,  and  those  of  the  pons  passing  through  it,  have 
been  considered.  It  remains  still  to  be  said  that  in  the  superior  levels  of  the 
pons  there  is  a  system  of  fibers  which  becomes  medullated  shortly  before 
birth,  rising  out  of  the  pontile  fibers  through  the  raphe,  and  then  emitting 
its  fibers  right  and  left  in  the  substantia  reticularis  of  the  tegmentum. 
According  to  Bechterew,  these  fibers  end  in  the  foremost  part  of  the  nucleus 
reticularis. 

Ganglia,  similar  to  those  of  the  pons,  are  scattered  on  both  sides  of  the 
raphe,  and  in  it  as  far  upward  as  the  tegmentum. 


CHAPTEE    XXV. 
FINAL  EEVIEW. 

THE  preceding  chapter  treats  of  the  tegmentum,  in  continuation  of  the 
subject  of  the  eighth  chapter. 

A  few  millimeters  anterior  to  the  last-described  sections  the  fibers  of 
the  crus  cerebri  appear  out  of  the  pons,  and  extend  to  the  cerebrum  as  the  pes 
pedunculi.  In  the  medulla  oblongata  the  pyramids  formed  the  single  factor 
in  the  formation  of  the  crus;  but  from  the  pontile  ganglia  are  developed  the 
thick  tracts,  which  extend  in  the  median  and  lateral  divisions  of  the  crus 
upward  to  the  temporal  lobe  and  to  the  frontal  and  parietal  cortex. 


Fig.  254. 


Fig.  255. 


Fig.  256. 


Three  sections  through  the  pons  and  corpora  quadrigemina  of  a  newborn 
child,  demonstrating  the  course  of  the  cerebellar  peduncles  and  the  lemniscus. 
The  latter  lies  closely  above  the  pontile  fibers;  the  peduncles  (B,  Fig.  254) 
appear  farther  internal  in  Fig.  255,  and  their  decussation  begins,  and  in  Fig. 
256  is  at  its  greatest.  Heematoxylin  stain. 


There  appears  at  this  level  in  the  crura,  between  the  tegmentum  and 
the  crusta,  and  separating  them,  the  substantia  nigra. 

The  peduncles  of  the  tegmentum  are  lost  in  the  red  nucleus.  In  the 
place  of  the  velum  medullare  anticum  the  corpora  quadrigemina  form  the 
roof. 

A  few  schematic  representations  may  elucidate  the  manner  of  transi- 
tion from  the  pons  to  the  midbrain. 

26  (401) 


402 


ANATOMY    OF    THE    CEXTEAL    NERVOUS    SYSTEM. 


The  symptoms  appearing  in  affections  of  the  pons  and  oblongata  form, 
in  their  various  groupings,  the  proofs  of  the  anatomical  relations,  herein 
described. 

In  a  small  compass  are  collected  here  the  most  important  paths  for  the  move- 
ments of  the  body-muscles,  for  sensation,  for  the  movements  in  speech,  for  those 
concerned  in  deglutition,  etc.  A  lesion  needs  not  to  be  very  large  here  to  produce 
the  most  varied  symptoms. 

The  central  motor  and  sensory  tracts,  arising  in  the  cerebral  cortex,  in  the 
thalamencephalon  and  mesencephalon,  extend  through  the  pons  and  oblongata,  giv- 
ing off  there  only  such  fibers  as  pass  to  the  nuclei  of  the  cranial  nerves. 

Since  interruption  to  these  long  tracts  produces  the  same  symptoms,  no  matter 
if  it  occur  in  the  forebrain,  midbrain,  or  after-brain, — namely,  anaesthesia  or  paraly- 
sis on  the  opposite  side, — it  is  important  to  remark  that  one  may  only  sus- 


Fig.  257. — Position  of  the  nuclei  of  the  cranial  nerves.  The  oblongata  and 
pons  to  be  imagined  as  transparent.  The  nuclei  of  origin  (motor),  black;  the 
end-nuclei  (sensory),  red. 


pect  a  lesion  of  the  sensory  or  motor  paths  in  the  pons  oblongata  when  simultane- 
ously there  are  present  symptoms  which  indicate  that  one  or  more  cranial  nerve- 
nuclei  are  involved. 

Muscular  atrophy,  which  appears  only  in  affections  of  the  nuclei,  must  be  care- 
fully sought,  if  it  requires  to  locate  the  place  and  extent  of  such  an  affection.  Fig. 
257,  representing  the  position  of  the  nuclei  in  a  longitudinal  section  of  the  oblongata, 
facilitates  in  such  localization  rather  more  than  the  preceding  cross-section. 

Speech,  respiration,  and  deglutition  will  be  probably  disturbed  by  an  affection 
of  the  oblongata;  paralysis  of  mastication  (motor  part  of  the  trigeminal),  of  the 
facial,  or  of  the  abducens,  by  one  of  the  pons. 

But  since  the  central  fibers  going  to  the  centers  of  the  oblongata  pass  through 
the  pons,  affections  of  the  latter  may  occasionally  provoke  troubles  of  deglutition,  etc. 

The  motor  paths  to  the  extremities  lie  ventral  in  the  pyramids,  and  do  not 
pass  over  to  the  other  side  until  much  later,  just  above  the  spinal  cord.  The  motor 


FINAL    BEVIEW.  403 

fibers  for  the  cranial  nerves,  however,  lie  near  the  median  line,  ascend  in  the  raphe 
of  the  tegmentum,  and  cross  over  in  proximity  to  their  respective  nuclei. 

A  disease-focus  in  the  pons  will  affect,  accordingly,  in  the  majority  of  cases, 
the  opposite  extremities,  but  the  facial,  abducens,  or  trigeminal  of  the  same  side  as 
itself. 

Fig.  258  may  show  better  than  words  this  most  important  symptom  of  many 
lesions  of  the  pons  and  medulla,  viz.:  crossed  paralysis.  It  represents  the  motor 
supply  to  the  nerves  of  the  face  and  extremities.  It  will  be  seen  that  a  lesion  at 
A.  in  the  cerebrum,  or  in  the  right  pes  cerebri,  would  paralyze  the  left  facial  and  the 
left  extremities;  but  that  one  at  B,'in  the  territory  of  the  pons  on  the  right  side, 
would  paralyze  the  left  extremities  as  before,  but  may  affect  the  right  facial;  again, 
that  such  a  lesion  extending  slightly  over  the  middle  line  might  render  both  facials 
and  the  extremities  of  one  side  helpless.  It  will  also  be  seen  that  a  lesion  in  the 
pons  at  C  may  affect  the  fibers  going  to  the  opposite  side  of  the  face  as  well  as 
those  to  the  opposite  extremities,  not  producing  an  alternating  hemiplegia,  but  a 
direct  one,  just  as  if  situated  higher  in  the  cerebrum.  Crossed  hemiplegia  can  only 
be  produced,  except  when  there  are  several  lesions  present,  by  affections  of  the 
pons  or  by  tumors,  etc.,  located  ventrally  to  the  pons,  destroying  the  cranial  nerves 
in  their  periphery  and  the  pyramidal  tracts.  Since,  besides  the  facial,  the  nuclei  of 
the  sixth  and  fifth  nerves  lie  in  the  pons,  it  follows  that  they  also  may  partake  in 
the  varied  forms  of  paralysis  induced  by  pontile  lesions.  The  behavior  of  the  acusticus 
in  this  connection  is  not  clearly  understood. 

Through  the  pons  also  there  pass  fibers  to  the  nuclei  of  the  oblongata,  which 
preside  over  the  muscles  concerned  in  speech.  In  this  way,  with  affections  of  the 
pons  and  bulb,  there  arise  at  times  disturbances  of  speech,  while  the  power  of  speech 
remains  intact.  This  symptom  is  called,  according  to  its  severity,  dysarthria,  or 
anarthria. 

Lesions  in  the  tegmentum  of  the  pons  and  the  bulb  may  also  lead  to  disturb- 
ances of  sensation.  We  have  reason  to  believe  that  the  central  sensory  paths  lie  in 
the  lemniscus,  and  that  the  median  fillet  especially  contains  those  fibers  which  serve 
the  very  important  static  sensation.  Accordingly,  after  interruption  of  the  inter- 
olivary  tract  in  the  oblongata  light  disturbances  of  the  muscular  sense  are  observed. 
But  later  clinical  investigations  make  it  appear  probable  that,  at  least  in  the  bulb,  the 
tracts  for  cutaneous  tactile  sensation  do  not  lie  in  the  median  portion,  but  belong 
to  the  long  tracts,  lying  external  to  the  interolivary  tract.  In  the  pons,  also  laterally 
located  lesions  may  produce  crossed  sensory  disturbances.  If  the  lesion  be  some- 
where in  the  tegmentum  of  the  bulb  or  pons,  it  affects  not  only  those  central  tracts, 
which  pass  to  nuclei  of  the  opposed  side,  but  also  the  peripheral  parts  of  many  sen- 
sory nerves.  For  instance,  a  lesion  located  laterally  in  the  oblongata  may  encounter 
on  the  right  side  the  ascending  trigeminal  root,  and  the  crossed  sensory  tracts,  re- 
sulting in  right-sided  facial  and  left-sided  body  anaesthesia. 

Generally  a  single  focus  does  not  destroy  all  the  central  and  peripheral  sensory 
tracts;  hence  occasions  no  such  complete  hemianesthesia  as  occurs  with  disease  of 
the  centrum  ovale.  One  or  another  nerve  remains  usually  free.  This  is  especially 
true  of  the  taste-tracts  and  of  the  auditory  tracts,  in  which  complete  intrapontile 
interruption  to  the  conducting  paths  has  been  seldom  known. 

If  a  lesion,  relatively  large,  is  located  anywhere  near  the  median  line,  there 
may  result  naturally  double  hemianesthesia:  at  all  events,  a  rare  occurrence. 

Difficulties  of  mastication  and  of  deglutition  are  observed  since  the  motor  tri- 
geminal, the  glosso-pharyngeal,  and  hypoglossal  nuclei  are  easily  involved. 


404 


ANATOMY    OF    THE    CENTRAL   NERVOUS    SYSTEM. 


It  is  often  difficult  to  decide  whether  a  disease-focus  be  located  in  the  oblongata 
or  in  the  pons.     By  reason  of  the  position  of  the  motor  vagus,  spinal  accessory  and 


m 


Fig.  258. — Schema  of  the  motor  path  for  the  facialis  and  the  nerves  to  the 
extremities.  Frontal  section  through  the  cerebrum,  pes  pedunculi,  pons,  ob- 
longata, and  spinal  cord.  Rinden-Centren  filr  die  Extrem.itaten—ftir  das  Gesicht, 
Cortical  centres  for  the  extremities, — for  the  face. 


FINAL    REVIEW.  405 

glosso-pharyngeal  nuclei,  hoarseness,  aphonia,  and  respiratory  troubles  are  observed 
principally  only  in  lesions  of  the  oblongata.  Speech-difficulties— dysarthria,  an- 
arthria  (nucleus  nervi  hypoglossi) — and  circulatory  disturbances  occur  also  more 
often  in  affections  of  the  oblongata. 

Nearly  all  those  symptoms  can,  in  rare  cases,  be  caused  by  troubles  of  the 
cerebrum,  since  lesion  of  the  central  course  of  the  cranial  nerve-fibers  leads  to  paraly- 
sis the  same  as  that  of  the  nuclei  or  the  peripheral  nerves  themselves.  Paralysis  of 
the  various  muscles  supplied  by  nerves  from  the  bulb  can  only  with  certainty  be 
referred  to  a  lesion  in  the  oblongata,  when  accompanied  by  muscular  atrophy  and 
when  destruction  of  the  respective  nerve-trunk  after  its  exit  from  the  central  axis 
can  be  excluded. 

In  the  presence  of  cases  which,  through  a  combination  of  symptoms, — partici- 
pation of  widely-spread  tracts  and  only  certain  cranial  nerves,  alternating  sensory 
or  motor  symptoms,— suggest  that  the  lesion  must  be  in  the  oblongata  or  the  pons, 
it  will  be  serviceable  to  study  the  illustrations  given  above,  to  determine  whether 
there  is  any  place  whose  destruction  might  cause  all  the  symptoms.  In  this  way  it 
will  be  possible  in  many  cases  to  determine  fairly  exactly  the  location  and  size  of 
the  lesion.  It  should  not  be  forgotten,  however,  to  consider  the  basal  aspect  of  the 
brain,  as  there  disease-processes  may  produce  pressure  on  the  longer  tracts  as  well  as 
destruction  of  the  nerve-trunks. 

With  this  we  have  practically  finished  our  task.  A  large  number  of  im- 
portant fiber-systems  have  been  studied  in  their  relations  to  the  central  gray 
masses,  and  in  their  course  from  the  cerebrum  to  near  the  end  of  the  mid- 
brain,  or  from  the  spinal  cord  upward  to  about  that  point.  But  it  may  be 
of  assistance  to  consider  certain  ones  again  briefly  in  their  interrelationships, 
because  they  are  of  particular  interest  physiologically  and  pathologically,  or 
because  the  general  view  of  their  relations  to  each  other  was  impeded  by  the 
interruption,  after  Chapter  XX,  of  the  series  of  investigation,  due  to  didactic 
interests. 

The  following  is,  then,  in  the  nature  of  a  repetition:  a  short  representa- 
tion to  be  used  with  the  illustrations: — 

1.  The  motor  nerves  are  the  continuations  of  the  axis-cylinders  of  the 
great  ganglion-cells  in  the  motor  nuclei  of  the  spinal  cord  and  brain. 
Around  these  ganglion-cells  arborize  the  terminals  of  the  central  motor 
paths.    These  run,  at  least  to  a  large  extent,  in  the  pyramidal  tracts. 

2.  The  pyramidal  tracts,  the  most  important  of  the  motor  paths,  arise 
from  the  upper  two-thirds  of  the  central  convolutions  and  the  paracentral 
lobule  and  extend  downward  to  a  place  just  behind  the  knee  of  the  internal 
capsule.    From  there  they  enter  the  pes  cerebri,  occupying  its  middle  third. 
Below  this,  in  the  pons,  their  fibers  are  but  little  separated  by  transverse 
fibers.    When  they  emerge  from  the  pons  their  fibers  form  two  large  bundles 
in  the  ventral  portion  of  the  medulla  oblongata.     So  they  descend  to  the 
spinal  cord,  where  the  larger  portion  of  their  fibers  crosses  over  to  the  lateral 
column,  while  a  smaller  portion  (anterior  pyramid)  remains  on  the  same  side. 
Both  tracts  enter  into  relationship  with  the  cells  of  the  anterior  horn  of  the 


406  ANATOMY    OF    THE    CEXTEAL   NEEVOUS    SYSTEM. 

side  opposite  to  the  origin  of  the  pyramids  in  the  cortex,  by  means  of  col- 
laterals.   From  the  cells  in  the  anterior  horns  arise  the  motor  roots. 

3.  The  central  path  for  the  motor  cranial  nerves  is  better  known  for 
the  facial  and  hypoglossal. 

The  facial  tract  arises  in  the  region  of  the  lower  third  of  the  central 
convolutions,  probably  only  for  its  lower  branches,  the  source  of  the  frontal 
part  of  it  being  unknown  (gyrus  angularis?);  extends  from  there  inward 
transversely  over  the  nucleus  lentiformis,  and  arrives  very  close  to  the  py- 
ramidal tract  in  the  internal  capsule.  At  any  rate,  in  the  pes  cerebri  it  is 
clinically  not  distinguishable  from  the  pyramid.  Its  fibers  then  leave  the 
general  motor  tracts  probably  with  the  familiarly  called  '^bundle  from  the 
crusta  to  the  tegmentum."  Certain  it  is,  that  in  the  pons  it  is  separated 
from  the  other  motor  paths  (see  Fig.  258).  How  it  reaches  the  nucleus  is 
as  yet  unknown.  But  it  finally  arrives  at  the  crossed  facial  nucleus  in  the 
inferior  portion  of  the  pons.  From  this  arises  the  nerve. 

In  the  most  ventral  part  of  the  anterior  central  convolution  probably 
lies  the  cortical  area  for  the  hypoglossus.  From  this  region,  at  least,  there 
passes  downward  a  bundle,  ventrally  to  the  facial  fasciculus,  whose  interrup- 
tion has  caused  at  times  bilateral  hypoglossal  disturbances.  As  it  extends 
from  the  cortex  to  the  capsula  interna  it  passes  over  the  upper  edge  of  the 
nucleus  lentiformis,  and  must  lie  in  close  proximity  to  the  speech-fibers  just 
external  to  the  beginning  of  the  tail  of  the  caudate  nucleus.  In  a  case 
observed  by  the  writer,  a  focal  lesion  of  about  the  size  and  thickness  of  a 
dime  interrupted  both  tracts  at  this  place.  In  the  capsule  the  hypoglossal 
fibers  probably  run  between  those  of  the  facial  and  those  for  the  extremities. 
Within  the  pons  its  fibers  must  be  separated  from  the  pyramid,  and  probably 
pass  in  the  above-named  bundle  median  to  the  fillet,  posteriorly  and  upward 
in  the  raphe.  It  joins  the  opposite  nucleus  (and  that  of  the  same  side?)  after 
reaching  the  oblongata,  and  from  the  nucleus  arises  the  nerve. 

4.  The  motor  speech- tract.     Of  this  we  know  certainly  but  few  facts: 
the  starting-point  in  the  lower  frontal  convolution,  the  termination  in  the 
nuclei  of  the  facial  and  hypoglossal,  and  an  intermediate  point,  lying  exter- 
nal to  the  tail  of  the  caudate  nucleus.    Probably  (Wernicke)  this  tract  ex- 
tends from  Broca's  convolution — the  inferior  frontal — somewhat  internally 
and  in  a  nearly  horizontal  direction  dorsal  to  the  capsula  externa,  under 
cover  of  the  insula.     Its  fibers  then  arrive  in  the  portion  of  the  internal 
capsule  posterior  to  the  general  motor  paths  and  then  in  the  pes  cerebri.    In 
the  pons  they  must  rise  gradually  out  of  the  crusta  and  into  the  tegmentum. 
In  all  of  these  places  mentioned  disease  produces  disorders  of  speech. 

Every  motor  nerve  then  arises  in  a  nucleus  in  the  central  organ.  The  nerve 
and  its  nucleus  form  the  first  division  of  the  path;  to  the  nucleus  there  extends 


FINAL   EEVIEW.  407 

from  the  cortex  of  the  cerebrum  the  converging  pyramidal  fibers,  as  the  second 
division  of  the  chain:  nerve.,  nucleus— pyramidal  tract,  cortex. 

As  long  as  the  first  division  remains  intact,  the  corresponding  muscles  may  be 
made  to  contract  by  electric,  mechanical,  and  reflex  irritation  in  animals,  even  also 
to  a  certain  degree  by  voluntary  impulse;  if  nerve  or  nucleus  be  destroyed,  how- 
ever, positive  paralysis  results. 

To  a  complete  voluntary  ability  it  is  necessary  that  both  divisions  be  sound; 
indeed,  with  the  highly  developed  brain  of  man  when  the  second  division  is  inter- 
rupted there  is  no  movement  possible  as  a  result  of  the  will.  When  one  suffers  a 
stroke  of  apoplexy  with  tearing  of  the  internal  capsule,  the  muscles  of  the  opposite 
side  of  the  body  are  not  really  paralyzed;  they  can  no  longer  be  brought  into  con- 
traction by  the  will,  but  may  by  other  means.  It  is  different  when  in  infantile 
spinal  paralysis,  for  example,  a  nucleus  itself  is  destroyed;  then  follows  a  real 
paralysis,  which,  generally  irreparable,  leads  to  atrophy,  and  reacts  but  little  to 
reflex  or  other  stimulation.  It  makes  a  great  difference  as  to  the  prospect  of  the 
recovery  of  function  whether  the  cerebral  tract  be  interrupted  or  some  place  lower 
down. 


5.  The  coronal  fibers  to  the  pons  arise  from  the  cortex  cerebri,  espe- 
cially the  temporo-occipital  lobe;  perhaps  also  from  the  frontal  lobe.    They 
extend  through  the  internal  capsule  to  the  crusta  of  the  pes  and  then  to 
the  pons.    Experiments  made  by  the  degeneration  method  show  that  they 
extend  no  farther  than  to  groups  of  ganglion-cells  there  found.     But  to 
these  same  groups  one  can  trace  fibers  coming  from  the  opposite  half  of  the 
cerebellum  (cerebellar  peduncles). 

6.  The  sensory  nerves  arise  from  cells  in  the  spinal  ganglia.    At  least  in 
vertebrates  no  other  origin  has  been  demonstrated  for  them.    Since  we  know, 
however,  that  the  optic  and  olfactory  nerves  contain  fibers  which,  arising 
from  sense-epithelium,  pass  centrally;    since,  further,  it  has  been  shown 
in  invertebrates  that  there  are  fibers  arising  out  of  epidermal  sense-epithe- 
lium, it  were  not  impossible  that  there  should  be  fibers  in  sensory  nerves 
which  originated  in  the  periphery.    The  process  of  secondary  degeneration 
after  section  of  the  nerve  speaks  against  this  supposition. 

From  the  cells  of  the  spinal  ganglia  arises  a  second  tract:  the  spinal 
root,  which  enters  into  the  cord.  A  part  of  the  root  splits  up  in  the  pos- 
terior horns,  or,  it  may  be,  in  the  nuclei  of  the  cranial  sensory  nerves,  arbor- 
izing around  cells  (distal  nuclei  of  the  sensory  nerves). 

Another  portion  first  courses  a  distance  in  the  central  organ,  either 
upward,  as  the  spinal  nerve-fibers  of  the  posterior  columns,  or  downward,  as 
many  roots  of  the  cranial  sensory  nerves,  before  it  ends  in  distal  nuclei. 

From  the  cells  of  these  nuclei  arises  the  central  sensory  tract,  or  the  tract 
of  second  order.  It  arrives  either  at  the  level  of  the  entrance  of  the  root 
into  the  central  axis,  or  higher  up,  always  in  the  territory  of  the  decussated 
lemniscus.  But  it  extends  toward  the  cerebrum  with  the  lemniscus. 

7.  We  do  not  yet  know  the  cells  of  origin  nor  the  terminations  of 


408  ANATOMY    OF    THE    CENTRAL   NERVOUS    SYSTEM. 

the  sensory  paths  of  second  and  higher  order.  Those  of  higher  order  lie 
in  the  median  fillet  from  the  thalamus,  and  in  the  lateral  fillet  or  the 
fillet  of  the  corpora  quadrigemina. 

The  fibers,  arising  in  the  nuclei  of  the  posterior  columns,  perhaps  also 
those  arising  in  the  nuclei  of  the  spinal  cord,  extend  in  the  median  line 
within  the  lemniscus  tract  upward,  and  terminate  in  the  ventral  portion  of 
the  thalamus  opticus.  The  fibers  from  the  nucleus  of  the  trigeminus  have 
the  same  terminus,  but  they  extend  to  the  thalamus,  not  through  the  lemnis- 
cus tract,  but  more  dorsally  and  median.  Besides  the  ending  of  the  median 
fillet,  the  tegmental  radiation  from  the  parietal  lobe  also  ends  in  the  region 
of  the  thalamus.  By  it  is  established  a  connection  between  the  sensory  nerve 
and  the  parietal  lobe  of  the  brain.  It  presents  a  tertiary  sensory  path. 

The  tegmental  fibers  arise  in  the  parietal  lobe,  possibly  in  the  same  con- 
volutions as  the  pyramidal  fibers,  and  from  there  extend  to  the  posterior 
third  of  the  internal  capsule.  In  this  region  are  joined  to  them  the  visual 
radiation  of  the  occipital  lobe  and  the  central  auditory  path.  A  part  of  the 
tegmental  tract  extends  inward  (to  the  right).  A  second  portion  extends  to 
and  through  the  lentiform  nucleus;  another  arrives  at  the  thalamus. 

The  central  fibers  from  the  nuclei  of  the  cranial  nerves,  perhaps  also 
some  from  nuclei  of  the  spinal  nerves,  ascend  in  the  inferior  or  lateral  fillet. 
These  end,  in  large  part,  in  the  ganglia  of  the  corpora  quadrigemina,  and 
in  another  part  in  the  median  corpus  geniculatum,  here  principally  the 
acusticus  paths  of  higher  order. 

To  these  nuclei  passes,  principally  from  the  white  substance  of  the  tem- 
poral lobe,  but  also  from  more  anteriorly  situated  cortical  areas,  a  fibrous 
'tract,  the  cortical  path  of  the  acusticus,  etc. 

In  this  manner  all  the  various  fibers  of  the  lemniscal  tract  are  con- 
nected with  their  centers,  lying  on  that  side  which  is  crossed  to  the  lem- 
niscus. The  decussation  takes  place  in  the  oblongata  for  one  portion,  for 
another  in  the  cord  itself.  In  the  nuclei  terminate  always  the  fibers  of  the 
posterior  roots,  or  the  cranial  sensory  nerves. 

8.  A  portion  of  the  sensory  nerves  ends  in  the  neighborhood  of  Clarke's 
column  of  cells.    From  them  arises  the  direct  cerebellar  tract,  which  extends 
in  the  periphery  of  the  lateral  tract  of  the  cord  up  to  the  cerebellum. 

9.  Some  cranial  sensory  nerves  receive  additional  fibers,  coming  from 
the  cerebellum  (direct  sensory  cerebellar  tract). 

10.  The  cortical  area  and  the  central  path  of  the  sensory  portion  of  the 
nervus  trigeminus  from  the  cortex  to  the  capsula  are  yet  unknown.    Follow- 
ing pathological  experiences,  its  fibers  must  lie  in  the  posterior  third  of 
the  capsule.    The  cortical  tract  of  the  trigeminal  ends,  in  rabbits  at  least,  in 
the  ventral  portion  of  the  thalamus.     Leading  up  to  it  is  a  large  bundle 


FINAL    REVIEW.  409 

from  the  opposite  nucleus  of  the  bulb.  And  in  this  nucleus  itself  terminate 
the  processes  from  the  cells  of  the  G-asserian  ganglion. 

The  trigeminus  also  arises  in  part  from  nuclei  lying  in  the  central  organ 
itself.  So  far  we  know  two  of  these:  one  in  the  lateral  wall  of  the  aqueduct 
beneath  the  corpora  quadrigemina;  the  other,  the  so-called  motor  nucleus, 
lying  in  the  pons. 

The  ascending  root  contains  the  tactile  nerves  of  the  face,  as  is  shown 
by  pathology. 

11.  The  nervus  acusticus  is  conveniently  regarded  as  two  nerves:   the 
nervus  cochlearis  and  the  nervus  vestibularis. 

The  cortical  origin  of  the  nerve  of  hearing,  the  coclilear,  must  be  sought 
in  the  region  of  the  temporal  convolutions.  Clinical  observations  allow  the 
conclusion  that  from  there  a  tract  leads  to  the  inferior  portion  of  the  internal 
capsule,  and  probably  through  the  arm  of  the  posterior  corpus  quadri- 
geminum  to  its  gray  matter.  Thence  the  lateral  lemniscus  extends  down- 
ward toward  the  superior  olive  in  the  oblongata,  and  in  this  end  also  the 
fibers  from  the  nucleus  acustici  ventralis,  the  trapezoid  body.  In  this 
nucleus,  however,  arborize  the  end-branches  from  the  ganglion-cells  of  the 
ganglion  spirale  cochleae:  the  auditory  nerve-roots. 

About  the  central  course  of  the  nervus  vestibuli  but  little  is  known.  Its 
fibers,  coming  from  the  cells  of  the  macula  and  the  crista  acustica,  end 
partly  in  the  dorsal  nucleus  and  extend  partly  to  the  cerebellum.  Besides, 
this  nerve  contains  fibers  from  lower  levels  of  the  oblongata,  and  additions 
from  the  lemniscus  as  stria?  acustica?  (compare  description  given  previously). 

The  upper  olive,  with  which  not  only  the  cochlear,  but  also  the  ves- 
tibular,  stands  in  relation,  is  intimately  connected  with  the  nuclei  of  the 
motor  nerves  of  the  eye  and  with  the  cerebellum;  probably  also  with  the 
corpora  quadrigemina.  It  is  likely  that  it  belongs  to  the  equilibration- 
apparatus  of  the  body. 

The  trigeminus,  as  well  as  the  acusticus,  receives  fibers  from  the  cere- 
bellum. 

12.  Nothing  is  known  about  the  central  tract  of  the  vagus.     If  the 
much-mentioned  place  in  the  posterior  part  of  the  capsule  be  destroyed, 
vagus  symptoms  do  not  appear;   instead,  there  come  disturbances  of  taste 
(glosso-pharyngeus).    The  course  of  the  fillet-fibers  to  the  opposite  pneumo- 
gastric  and  glosso-pharyngeal  nuclei  has  been  mentioned.    Both  these  nerves 
also  probably  receive  additional  fibers  from  the  cerebellum. 

13.  The  central  course  of  the  options  has  already  been  considered  in  its 
relations. 

It  may  be  repeated  that  this  nerve  arises  from  the  pulvinar  thalami, 
the  corpus  geniculatum  laterale,  the  tuber  cinereum,  and  the  corpora  quad- 
rigemina; that  it  receives  fibers,  arising  in  the  retina,  which  end  in  the 


410  ANATOMY    OF    THE    CENTRAL    NERVOUS    SYSTEM. 

parts  of  the  brain  mentioned.  To  all  these  "primary  optic  centers"  come 
fibers  from  the  optic  radiations,  beginning  in  the  occipital  lobe.  These 
extend  along  the  lateral  side  of  the  posterior  horn,  and  under  the  inferior 
parietal  lobule,  on  their  way  from  the  cortical  origin  to  the  primary  optic 
centers.  From  this  fact  arise  visual  disturbances,  having  the  character  of 
cortical  lesions,  which  have  been  noticed  in  disease  of  this  lobule  or  by  ex- 
perimental lesion  of  the  corresponding  locus  in  animals. 

The  fibers  of  the  optic  tract  pass  to  the  chiasm.  There  the  larger 
portion  passes  to  the  opposite  side,  while  a  smaller  portion,  up  to  this  point 
not  separated  from  the  bundle,  remains  on  the  same  side.  The  long- 
cherished  dispute  about  the  chiasm  has  recently  been  decided,  as  stated 
above,  finally  and  convincingly  by  Singer  and  Munzer.  The  bundle  which 
does  not  cross  over  is  very  unimportant  in  some  animals,  and  is  entirely 
wanting  in  certain  orders.  In  the  latter  case  there  is,  accordingly,  a  total 
decussation. 

The  optic  tract  must,  in  addition,  contain  the  pupillary  fibers  from  the 
oculo-motorius.  It  has  not  yet  been  definitely  demonstrated  how  they  join  it. 

The  central  course  of  the  olfactorius  was  described  in  its  relations,  in 
Chapter  XIII.  Compare  especially  Fig.  144,  relating  to  this  subject. 


IXDEX  OF  AUTHOKS. 


The  figures  immediately  preceded  by  an  asterisk  (*)  refer  to  illustrations. 

Aeby,  13. 

Deiter,  17,  93,  108,  237,  329, 

Gehuchten,  Van,  12,  14,  21, 

Ahlborn,  11,  92. 

350,  359,  378,  391. 

*17,    115,    146,    154,    213, 

Aranzio,  E.,  3. 

Descartes,  13. 

214,  308,   *207,  329    359 

Arnold,  3,  4,  378. 

D6jSrine,   J.,    14,   240,   247, 

391. 

Arnold,  F.,  247,  329. 

272,  298. 

Gennari,  232-234. 

Arnold,  J.,  378. 

D6jerine  -  Klumpke,     Mad- 

Gerlach, 5,  20,  329,  359. 

Auerbach,  328. 

ame,  14. 

Gervais,  223. 

Dogiel,  25. 

Girgensohn,  10. 

Baginsky,     285,     387,     388, 

Donaldson,  55. 

Golgi,  5,  12,  *5,  *6,  20,  21, 

391. 

Dostojewsky,  281. 

131,  *117,  213,  229,  *151, 

Baillarger,  232,  247. 

Duval,  247,  378,  392. 

231,  247,  *207,  329,  352, 

Baudelot,  11. 

359,  378,  391. 

Beehterew,     14,     233,     329, 

Eberstaller,  223. 

Goll,  359. 

381,  383,  384,  391,  400. 

Ecker,  223. 

Goltz,  75,  155. 

Becker,  25. 

Eckhard,  4. 

Goronowitscli,  *39. 

Beevor,  240,  329. 

Edinger,  104,  146,  304,  309. 

Gotte,  10. 

Bellet,  7. 

Ehrenburg,  4. 

Gottsche,  11. 

Bellingeri,  359. 

Ehrlich,  5,  12. 

Cowers,  328,  350,  359. 

Bellonci,  5,  11,  20,  247,  309. 

Ellenburger,  223. 

Graf,  127. 

Bergmann,  329,  388. 

Engleman,  90. 

Grainger,  359. 

Bernheimer,  309. 

Erb,  216,  *222. 

Gratiolet,  10,  223. 

Berthi,  *17. 

Ewald,  44,  91,  226. 

Gudden,  7,  8,  138,  220,  247, 

Bethe,  13. 

Ewart,  35. 

*169,  274,  287,  294,  303, 

Bidder,  13. 

Exner,   5,   31,   33,   43,   356, 

306,  309,  378. 

Bielschofsky,  272. 

358. 

Guldberg,  223. 

Birge,  55,  *32. 

Bischoff,  223. 

Fallopia,  3. 

Haller,  20,  70. 

Blum,  264. 

Fere,  7,  14,  247. 

Hannover,  4. 

Bouchard,  6. 

Ferrier,  326,  328,  329,  337, 

Held,  378,  391. 

Bovce.  302,  350. 

350. 

Henle,   14,  *124,  *129,  247, 

Brandis,  12,  108. 

Flatow,  224. 

*215,  *231,  *232,  366. 

Bregmann,  6. 

Flechsig,  6,  7,  9,  10,  13,  210,    Henschen,  309. 

Brissaud,  7,  14,  247. 

240,    245,    246,   247,    257,    Herrick,  11,  148. 

Broca,  170,  213,  216,  223. 

271,    309,    349,    354,    359,    Herve,  223. 

Bruns,  331. 

391,  399.                                   Hirschfeld,  *205. 

Bumm,    12,    285,    387,   388, 

Flemming,  25. 

His,  10,  12,  16.  21,  36,  50, 

391. 

Flesch,  281. 

58,  84,  201,  287,  332,  359, 

Bunge,  *17. 

Flower,  *123,  223. 

378,  392. 

Burkhardt,  12. 

Forel,  6,  8,  21,  240,  271,  301,  1  Hoche,  246,  *228,  352. 

Burdach,  3,  4,  13,  223,  -247, 

306,  309,  391. 

Hodge,  25. 

329,  359,  378. 

Foville,  3,  4. 

Horsley,  Victor,  14. 

Freud,  378,  391. 

Hosel,  399. 

Carus,  11. 

Friedmann,  247. 

Huguenin,  14. 

Charcot,  6,  7,  247,  359. 

Fritsch,  von,  11,  *31,  70,  89, 

Charpy,  14. 

137,  *91. 

Jackson,  Hughlings,  238. 

Clarke,  L.,  5,  66,  247,  328, 

Froriep,  57-59. 

Jelgersma,  13. 

341,  349,  350,  359,  376. 

Fiirstner,  352. 

Jensen,  175. 

Cole,  97. 

Fusari,  115. 

Collins,  340. 

Kaes,  *153,  233. 

Cunningham,      *136,      205, 

Gall,  3,  4,  205,  294. 

Kahler,  14. 

223. 

Ganser,    8,    224,    287,    306, 

Kaufmann,  7. 

308,  309. 

Kayser,  55,  340. 

Darkschewitsch,    295,    365, 

Gaskell,  85,  87. 

Kei'bel,  287. 

378. 

Gaull,  334. 

Key,  319. 

(411) 

412 


INDEX    OF   AUTHORS. 


Koch,  377,  *240,  378.                 Onufrowicz,  240,  391. 

Sioli,  247. 

Kolk,  Van  der,  378.                  Osborn,  11. 

Singer,  7,  359,  410. 

Kolliker,    von,    10,    13,    14, 

Smith    Elliot    11,  211,  224. 

21,  104,  122,'  146,'  213,'  220',    Pansch,  223. 

So'mmering,  von,  3,  359. 

224,    247,    271,   275,    294,    Pellizi,  329. 

Spencer,  127. 

295,    309,    329,    359,    378,    Perlia,  309. 

Spitzka,   11,  224,   285,  295, 

380,  387.  391,  392. 

Perls,  206,  207. 

309,  399. 

Koppen,  11. 

Petit,  Francois,  377. 

Spurzheim,  3,  294. 

Krause,  W.,  14. 

Pick,  304. 

Stannius,  93. 

Krueg,  223. 

Picolhomini,  378. 

Starr,  304. 

Kukenthal,  198,  223,  224. 

Pincus,  97. 

Steiner,  48. 

Kupffer,   von,    10,    12,    *18, 

Pitres,  7,  247. 

Stieda,  11. 

57,  58,  60,  61,  128,  129. 

Purkinie,  104,  110,  329. 

Stilling,   Benedict,   4,   5,   6, 

13,    66,    *209,    324,    *210, 

Lenhossek,  von,  14,  *5,  21, 

Raim,  3. 

325,   329,    341,    359,    378, 

39,  *34,  341,  359,  392. 

Ramon  y  Cajal,  *5,  *6,  21, 

381. 

Leonowa,  341. 

104,    115,    236,    247,    308, 

Stilling,  J.,  287,  309. 

Leveille,  *205. 

329,  343,  356.                           Strang,  Oliver  S.,  97. 

Leuret,  10,  223. 

Ramon  y  Cajal,  P.,  115,  *94, 

Striimpell,  7,  348. 

Leemvenhoeck,  Van,  3. 

*116,  213,  *184,  287. 

Studniczka,  159. 

Lewis,  Bevan,  224,  247. 

Ramon  y  Cajal,  S.,   12,  14, 

Sylvius,  3. 

Ley  dig,  13. 

*9,  139,  146,  168,  213,  229, 

Symington,  211. 

Lowenthal,  7,  8,  224,  247, 

*152,  247,  275,  287,   311, 

350,  354,  359. 

*207,  326,   341,  359,   376, 

Tartuferi,  309. 

Ludwig,  13. 

378,  394,  397. 

Tenchini,  223. 

Luys,  14,  271. 

Ranvier,  16,  29,  30. 

Tiedemann,  4,  10. 

Redlich,  344. 

Treviranus,  11. 

Mahaim,  257,  272,  299. 

Reichert,  3,  4,  10. 

Tuczeck,  237. 

Malacarne,  3,  329. 

Reil,  3,  4,  190,  247,  329,  378, 

Tiirck,  6,  72,  359. 

Mann,  *149,  226. 

Reissner,  11. 

Turner,  216,  *145,  *146,  224, 

Marchi,    7,    246,    326,    329, 

Remak,  4,  337. 

326,  328,  329,  350. 

348,  *228,  352. 

Retzius,  5,  12,  21,  *8,  33,  34, 

Martin,  8,  392. 

39,  *15,  *16,  59,  *33,  319, 

Valentin    11. 

Martinotti,  229. 

391. 

Variolo   3 

Mason,  11. 

Richter,  224,  247. 

Mauthner,  70,  94. 
Mayser,  8,  11. 
Mendel,  14. 
Meyer,  11. 
Meynert,  5,  6,   13,   14,  223, 

Rietz,  240. 
Rolando,  3,  278. 
Roller,  377,  378,  391. 
Romanes,  35. 
Riickhardt,  11. 

V  esalius,  o. 
Viault,  11,  240. 
Vicq  d'Azyr,  3,  232. 
Vieussens,  3,  377. 
Vincenci,  380. 

224,  234,  247,   *169,  269,    Riidinger,  223. 
299,  309,  329,  376,  378. 
Michicho-Maklay,  11.                Sachs,  240,  247,  258. 

Wagner,  20,  205. 
Waldeyer,  21,  223,  339,  342, 

Mihalkovics,  von,  10,  *21. 
Minghazzini,  311,  326,  329. 
Monakow.  8.   21,   108,   139, 

Sala,  247. 
Santorini,  378. 
Saunders,  11. 

359. 
Wallenberg,  378.  396,  397. 
Waller,  6,  333. 

155,    244,    247,    257,    259, 

Schaffer,  234,  247,  352,  358. 

Weigert,    5,    17,    *6,    *151, 

260,    271,    272,    285,    287, 

Schaper,  104. 

236,  328,  343,  358. 

309,  328,  388,  391,  399. 
Mott,  7,  328,  350,  359. 

Schieffverdecker,  7. 
Schillers,  55. 

Wepfer,  3. 
Wertiicke,  14,  240,  247,  257, 

Miinzer,  359,  410. 
Muratow,  240. 

Schnopfhagen,  194. 
Schroeder,  378. 

271,  309,  406. 
Westphal,  7,  304,  309. 

Schultze,  F.  E.,  329,  352. 

Wiedersheim,  11. 

Nansen,  20. 

Schultee,  Max,  25. 

Willis,  Th.,  3. 

Negrini,  223.                              Schiitz,  260,  377. 

Nissl,  5,  6,  *6,  24,  25,  *150,  1  Schwalbe,  14. 

Zacker,  247. 

229,  260.                                   Schwann,  30,  342. 

Ziegler,  *137. 

Sernow,  224. 

Ziehen,  198,  223,  224. 

Obersteiner,    14,    329,    344, 

Sherrington,  7. 

Zuckerkandl,  170,  216,  217, 

398.                                            Siemerling,  309. 

223. 

IXDEX  OF  COMPARATIVE  NEUROLOGY. 


Only  nouns  are  indexed.     The  figures  immediately  preceded  by  an  asterisk  (*) 
refer  to  illustrations. 


Invertebrates. 
Coclenterata. 

epithelium,  sensory,  37,  39. 
Echinodernt  a  td . 

sea-urchin,  movement-complex,  35. 
Vermes. 

annelida,  movement-complex,  33. 
earth-worm,  angle-worm,  Liimbricus  ter- 

restris. 

epithelium,  sensory,  40,  *15. 
ganglia,  34,  *12. 
movement-complex,  33,  *12. 
nerves,  sensory,  39. 
neuraxons,  20. 
A  rthropoda. 

bee,  ganglion-cells,  25. 
crab,  cray-fish,  Astracus  fluviatiUs. 
ganglion,  abdominal,  26. 
nerve,  commissural,  28. 
neuraxons  and  dendrites,  22. 
system,  nervous,  26-28. 
ganglion,  supra-oesophageal,  102. 
Molhisca. 

neuraxons,  20. 
snail,  Pterotrachea. 

cells,  sensory,  of  epithelium,  39,  *15. 

Vertebrates. 

lower  vertebrates. 

association-fibers  of  medulla,  80. 
brain,  12,  163. 
cerebellum,  51,  104. 

arms  of,  109. 

peduncles,  106,  107,  108. 

vital  center,  110. 
cerebrum,  removal  of,  208. 
commissura  media,  260. 

posterior,  295. 
cord,  spinal. 

bundle,  longitudinal  lateral,  351. 

centers,  anterior  column,  68. 

effect  of  removal,  75,  100. 

efficiency  of,  47. 

ganglion-cells  of  white  substance,  73. 

root-fibers,  posterior,  356. 

size,  74. 

transition  to  medulla,  75. 
corpus  striatum,  153,  154. 
faro,  musculature,  95. 
fillet,  99. 


Vertebrates,  lower,  hypothalamus,  132,  137, 
138. 

interbrain,  effect  of  removal,  125. 

ganglia,  lateral,  129. 

relation  to  forebrain,  143,  144. 
to  tectum  mesencephali,  120. 
line,  lateral,  57. 
lobus  olfactorius,  146. 
mantle,  159. 
medulla  oblongata,  association-fibers,  80. 

frontal  end,  99. 

vital  centers,  100. 
midbrain,  51. 

ganglion  ventrale  tegmenti,  123. 

importance  of,  112. 

relation  to  interbrain,  125. 
muscles,  innervation  of,  37. 
nerve,  accessory  spinal,  85. 

branchial,  75. 

facial,  motor,  95. 
sensory,  59,  97. 

masseteric,  95. 

olfactory,  fibers,  215. 

optic,  119,  285. 

pneumogastric,  85. 

trigeminal,  59. 
nerve-roots,  cranial,  77,  84. 
nucleus  dentatus,  106. 

praetectalis,  114. 

tegmenti,  120,  122. 
polus  frontalis,  162,  163. 
saccus  vasculosus,  129. 
stratum,  deep  medullary,  301. 
tectum  mesencephali,  120. 
thalamus  opticus,  51,  132,  134.  136. 

nuclei  or  ganglia,  132,  133,  134,  136. 
tractus  brevis,  medulla,  80. 

cerebro-spinalis,  30. 

cerebello-tegmentalis,  109. 

habenulo-peduncularis,  276. 

tecto-thalamicus,  120. 

Fishes  (Pisces). 

ansa  lentiformis.  256. 

apparatus,  olfactory,  152. 

brain,  11,  154. 

canals,  sensory,  of  head,  59.  60,  95-97. 

cells,  pigmented,  nerve-endings,  42. 

center,  optic,  287. 

cerebellum,  warm,  102. 

(413) 


414 


IXDEX    OF    COMPARATIVE    XEUROLOGY. 


Vertebrates. 

fishes,    cerebellum,     fasciculi    to     sensory 

nerves,  327. 
chiasma,  optic,  142. 
cochlea,  91. 
cord,  spinal. 

column  of  Stilling-Clarke,  66. 

columns,  dorsal  or  sensory,  64,  65. 

fundaments,  88,  89. 
corpus  geniculatum  laterale,  287. 

striatum,  153,  158,  178. 
decussation,    optic,    relation    to    eves, 
140. 

vago-cerebellar  tract,  86. 

velum,  108. 

dendrites  of  ganglion-cells  of  cord,  73. 
epistriatum,  149. 
fasciculus  longitudinalis  posterior,  82, 

137. 
fibers,  arciform,  external,  99. 

arciform,  internal,  99. 

Mauthner's,  70. 
fibrae  acustico-spinales,  82. 
fillet,  71,  124. 
ganglion  habenulse,  130. 
hypothalamus,  137. 
interbrain,  125. 

layer  (stratum),  deep  medullary,  118. 
lobe,  frontal,  153. 

optic,  113. 
mantle,  153. 
medulla,  *39. 
midbrain,  base,  121. 

fibers,  123,  124. 

roof,  113. 
nerve,  facial,  sensory  fibers,  97. 

optic,  113,  139,  287. 

pneumogastric,  innervation,  63,  64, 
86,  89. 

trigeminal,  innervation,  89. 
nerves,  cranial,  number,  59. 
nucleus,  auditory,  ventral,  92,  93. 

cerebellar,  105,  106. 

cord,  spinal,  posterior  columns,  79. 
80. 

globosus  cerebelli,  106. 

hypoglossal,  87. 

lateral,  of  midbrain,  121. 

magno-cellularis  strati  grisei,  132. 

of  nerves,  cranial,  84. 

pneumogastric,  motor,  87. 
sensory,  86. 

rotundus,  132. 

plate,  cerebellar,  cells  of,  104. 
radiation,  occipital   (?),  245. 
roots,  dorsal,  spinal,  63,  64. 
smell,  sense  of,  158. 
stratum  (layer),  deep  medullary,  301, 

302. 
supply,  sensory,  from  cranial  nerves, 

63,  64. 

torus  semicircularis,  302. 
tractus  cerebello-spinalis,  71. 

cord  to  cerebellum,  101. 
midbrain,  98. 


j  Vertebrates. 

fishes,  tractus,  cortico-olfactorius  (?),  151. 
int«rbrain  to  cerebellum,  101. 
midbrain  to  cerebellum,  101,  104. 
opticus,  124. 

strio-thalamicus,  157,  274. 
thalamus  to  cerebellum,  104. 
vago-cerebellaris,  86. 

vermis  cerebelli,  102. 
Acipenser  ruthenus,  see  sturgeon. 
alburmis      (carp      family),      cutaneous 

nerve-reticulum,  *17. 
ammocoetes,  see  also  petromyzon. 

ganglia  (nuclei)  of  cranial  nerves,  61. 
amphioxus,  encephalon  (?),  48. 
angler-fish,  innervation  of  head,  88,  89. 
Barltus  flnvia  tills,  barbel. 

brain,  sagittal  section,  *86,  *95. 

medulla,  section,  *52,  *53,  *54. 

root,  pneumogastric,  *52,  *53,  *54. 

trigeminal,  *52,  *53,  *54. 
carcJiarias,  shark,  brain,  *106. 
carp,    lateral    olfactory    fasciculus,    149, 

150. 

Cephalopt&ra  lumpus,  ray,  medulla,  41. 
cod-fish,  Gadus  cegleflnis. 

brain,  *38,  77,  *63,  154. 

cord,  spinal,  74. 

medulla,  112. 

midbrain,   112. 
cyclostomes,  Cyclostomata. 

cerebellum,  101. 

cord,  spinal,  medullated  fibers  in  gray 
matter,  70. 

"dorsal  cells,"  73. 

ganglion-cells  of  medulla,  18. 

mantle,  145,  159. 

medulla,  nuclei,  18. 

nerves,  cranial,  number,  61. 

nerve-tracts,  12. 

nuclei  of  medulla,  cells,  18. 
cyprinoids,  carps. 

brain  and  cord,  sagittal  section,  *44, 
86. 

nerve,  facial,  sensory,  97. 
Cyprinus  auratus,  gold-fish. 

brain,  horizontal  section,  *98. 

medulla,  frontal  section,  85,  *45. 
dipnoans  (Dipnoi). 

canals,  sensory,  of  head,  95-97. 

cerebellum,  101. 

tela  chorioidea,  127. 
eel,  electric,  malapterurus,  gymnotus. 

cord,  spinal,  ventral  columns,  64,  *31. 

ganglion-cells,  18,  20. 

nucleus  nervorum  electricorum,  66. 

organ,  electric,  20,  66. 

tractus  cerebello-spinalis,  71. 
Galeus  canis,  shark,  brain,  106. 
ganoids  (Ganoidei),  see  also  sturgeon. 

mantle,  160. 
Gobio  flui'iatilis,  gudgeon. 

thalamus   opticus,   horizontal   section, 

•91. 
gold-fish,  Cypriniis  auratus,  medulla,  85. 


IXDEX    OF    COMPARATIVE    NEUROLOGY. 


415 


Vertebrates. 

fishes,  GymnntuK,  see  eel,  electric. 
Leuciscus  rutllus,  see  white-fish. 
Lophius  piscatorius,  see  angler-fish. 
Malapterurtis,  eel,  electric, 
ganglion-cells  of  cord,  18. 
minnow,  see  Phoxinus  Icevis. 
Perca  flutiatilis,  perch. 
bulbus  olfactorius,  148. 
corpus  striatum,  *96. 
petromyzon. 

brain,  Ahlborn's  description,  11. 

ganglion  habenulae,  129. 

hypophysis,  128,  129. 

interbrain,  125. 

lamina     commissuralis     mesencephali, 

118. 

mantle,  51. 

petromyzon  lai-va,  ammocoetes. 
ganglia,  cranial,  *26b,  *26c,  61. 

epibranchial,  *26&,  *26c,  61. 
nerves,  cranial,  *26&,  *26c,  61. 
Phoxinttx  la? vis.  minnow. 

cerebellum,  cells  of  Purkinje,  *62. 
layer,  granular,  *62, 
zona  molecularis,  *62. 
Raja  clavata,  see  ray. 
Raja  miralct us,  see  ray,  brain,  *106. 
rays,  brain,  sagittal  section,  *55,  *122. 
cerebellum,  sagittal  section,  *58. 
electric,  see  torpedo. 
forebrain,  ventricle,  159. 
hypophysis,  horizontal  section,  *78. 
mantle,  159,  161,  162. 
medulla,  frontal  section,  *41,  79,  82. 
Rhodeus  amarus  (carp  family), 
chiasma,  optic,  section,  *70. 
midbrain,  frontal  section,  *68. 
Scyllium  canicula,  shark, 
brain,  horizontal  section,  *92. 
interbrain,  143,  144. 
midbrain,  frontal  section,  *59,  *89. 
thalamus  opticus,  frontal  section,  *93. 

horizontal  section,  *90. 
selachians  (Selachii),  see  also  rays  and 

sharks. 

aqueduct  of  Sylvius,  113. 
brain,  anatomy,  11,  *106. 

sagittal  section,  *108. 
cerebellum,  101. 

layer,  medullary,  104. 

plate,  102. 

relation  to   fibrse   arcuatse   internee. 

108. 

commissura  ventralis,  70. 
decussatio  transversa,  138. 
epiphysis,  127. 
forebrain,  ventricle,  159. 
lobus  cerebellaris  acustici,  105. 

trigemini,  105. 
mantle,  145,  159,  161. 
nerve,  optic,  113. 
nucleus  lateralis,  121. 
oliva  superior,  auditory  fibers,  93. 
pallium,  hemispheres,  159. 


Vertebrates. 

fishes,  selachians,  recessus  mamillaris,  129. 

tracts  of  spinal  cord,  71. 
sharks,  see  also  carcharias,  scylUum,  and 

selachians. 

brain,  horizontal  section,  *92. 
cord,  spinal,  section,  *36c. 
fundaments  of  Froriep,  *26a. 

of  Kupffer,  *26a. 
interbrain,  sagittal  section,  infundib- 

ulum,  *77,  143,  144. 
lobes,  olfactory,  159. 
mantle,  159. 

midbrain,  frontal  section,  *59,  *89. 
thalamus,  frontal  section,  *93. 

horizontal  section,  *90. 
sturgeon,  brain,  larval,  sagittal  section, 

*18,  49. 

i    cerebellum,  *39. 

fasciculus  longitudinalis  posterior,  82. 
fundament  for  second  mouth,  129. 
hemispheres  (?),  50. 
hypophysis,  128,  129. 
medulla,  *39. 

nucleus  of  pneumogastric,  85,  86. 
pallium,  51. 
teleosts  (Teleostei). 
brain,  11,  84. 

schematic,  sagittal  section,  *107. 
bulb,  olfactory,  147. 
cerebellum,  101,  109. 

association-fibers,  1 10. 

decussation-fibers,  109. 

fibrae  arcuatse  extern®,  108. 

layer,  medullary,  104. 
molecular,  105. 

surface,  105. 

chiasma,  optic,  section  through,  *70. 
commissura  ansulata,  118. 

ventralis,  70. 

corpus  striatum,  155,  158. 
decussation,  tegmental.  118. 

trochlear,  109. 
fasciculus    lateralis    olfactorius,     149, 

150. 
fibers  of  association,  cerebellum,  110. 

decussation,  cerebellum,  109. 
forebrain,  frontal  section,  *102,  *105. 
hemispheres,  154. 
hypothalamus,  156. 
line  lateral,  innervation,  93. 
lobus  cerebellaris  acustici,  105. 

trigemini,  105. 
mantle.    51,    145,    146,    155,    158,    159, 

160. 

medulla,  112. 
midbrain,  frontal  section,  *68,  *85. 

relation  to  cerebellum,  121. 

roof-segment,  113. 

size,  112. 
nerve,  facial,  sensory,  97. 

optic,  84. 

trochlear,  decussation,  109. 
oliva  superior,  auditory  fibers,  93. 
radiation,  occipital  (?),  245. 


416 


IXDEX    OF    COMPARATIVE    NEUROLOGY. 


Vertebrates. 

fishes,  teleosts,  sight,  midbrain,  176. 
smell,  176. 

stratum  medullare  profundum,  118. 
thalamus   opticus,   horizontal   section, 

•91. 

torus  semicircularis,  121. 
traetus  acustico-spinalis,  nucleus,  93. 
nucleo-cerebellaris    nervi    trigemini, 

109. 

vagi,  109. 
of  spinal  cord,  71. 
opticus,  176. 

strio-hypothalamicus,  156. 
strio-thalamicus,  154,  155. 
thalamencephalo-cerebellaris,  107. 
valvula  cerebelli,  105. 
vision,  physiology  of,  176. 
torpedo,  lobe,  pneumogastric,  cells,  89. 
lobus  electricus,  *48. 
medulla,  section,  *48. 
nucleus,  pneumogastric,  *48. 
organ,  electric,  90. 
trigla  (a  teleost). 

cord,  spinal,  columns,  64. 
cross- section,  *30,  85. 
trout-embryo,    brain,    sagittal    section, 

*55,  *107. 
mantle,  161. 

white-fish,  Leuciscus  rutilus,  roach, 
cord,  spinal,  columns,  64. 
cross- section,  64,  *29A. 
roots,  dorsal,  64. 

Zofirces     viviparus,    midbrain,     frontal 
section,  *85. 

Amphibians  (Amphibia). 

apparatus,  olfactory,  150. 
aqueduct  of  Sylvius,  113. 
brain,  11. 

cross-section,  167. 

sagittal  section,  *37,  *55,  *64,  *109. 
canals  of  head,  sensory,  59,  60,  95-97. 
centers,  optic,  287. 
cerebellum,  101. 

afferent  fibers,  104. 

surface,  105. 

corpus  geniculatum  laterale,  287. 
cortex,  olfactory,  170. 

cerebral,  physiology,  202. 

structure,  168. 
decussatio  transversa,  138. 

veil,  108. 

dendrites,  ganglion-cells,  73. 
epiphyses   (parietal  eye),  127. 
fasciculus  longitudinalis  posterior,  82. 
fibers  (fibrae),  acustico-spinales,  82. 

arciformes  externse,  99. 

Mauthner's,  70. 
forebrain,  167. 
formatio  bulbaris,  147. 
fovea  limbica,  162. 
ganglion  habenulse,  130. 
gyrus  marginalis,  202. 
hemispheres,  161,  162,  165. 


Vertebrates. 

amphibians,  interbrain,  126. 

mantle,  145,  146,  152,  160,  161. 

neuraxons  of  ganglion-cells,  168. 
medulla,  77,  78. 
midbrain,  base,  116. 

layer     (stratum),    deep    medullary, 

'116,  302. 

nerves,  cranial,  number,  59. 
facial,  sensory,  59,  60. 
optic,  113,  116,  287. 
pneumogastric,  innervation  of  skin, 

86. 

nucleus,  auditory,  ventral,  92,  93. 
hypoglossal,  87. 
of   columns,   posterior,   spinal   cord, 

79. 

pneumogastric,  motor,  87. 
oliva  inferior  (?),  98. 
polus  temporalis,  162. 
tela  chorioidea,  127. 
tract    (traetus),    cord    to    cerebellum, 

iqi. 

cortico-olfactorius,  151. 
interbrain  to  cerebellum,  101. 
midbrain  to  cerebellum,  101. 
olfactorius  septi,  166. 
olfactory,  149. 
optic,  287. 

strio-thalamicus,  155. 
tubercle    (tuberculum),   auditory,   92, 

93. 

amblystoma,  see  siredon. 
anura.  brain  and  cord,  179. 
axolotl,  see  siredon. 
bufo,  see  toad, 
frog,    bulb,    olfactorv,    sagittal    section, 

*94. 

cells,  epithelial,  nerve-endings,  42. 
cord,  spinal,  number  of  ganglion-cells, 

*32. 

increase  of  cells.  55. 
gingiva,  nerve-endings,  17. 
labyrinth,  loss  of,  44. 
mantle,  section,  *116. 
midbrain,  section  of  roof,  *66. 
Salamandra  maculata,  medulla,  *40. 
Siredon,  midbrain,  sagittal  section,  64. 
toad,  diencephalon,  *76. 

midbrain,  cross-section,  *69. 
triton,  brain,  sagittal  section,  *80. 
fibers,  arciform,  81. 
medulla,  cross-section,  *42. 
urodela,  brain  and  cord,  179. 

Reptiles  (Reptilia). 

apparatus,  olfactory,  150,  174. 

schema,  *101. 
area  parolfactoria,  165. 
body,  inferior  olivary  (?),  98. 

restiform,  99. 
brain,  11,  55,  177. 

olfactory,  212. 

sagittal  section,  *25,  *110,  *123. 
centers,  optic,  287. 


INDEX   OF    COMPARATIVE    NEUROLOGY. 


417 


Vertebrates. 

reptiles,  cerebellum,  101,  103. 

afferent  fibers,  104. 

fibrse  arcuatse  internse,  108. 

peduncles,  inferior,  99. 

surface,  105. 

column  of  Stilling-Clarke,  66. 
commissura  anterior,  brain,  153. 
cord,  359. 
grisea  thalami,  132. 

Meynert's,  260. 
conarium,  276. 
corona  radiata,  176. 
corpus  geniculatum  laterals,  133. 

striatum,  effect  of  removal,  156. 
cortex,  cerebral,  168,  176. 

association-bundles,  176. 

fundament  of,  168. 

olfactory,  169,  170. 

physiology  of,  174,  202. 

structure,  168. 
decussation  of  the  velum,  108. 

optic,  140. 

trochlear,  108. 
epiphysis,  127. 
epistriatum,  149. 
fasciculus      longitudinalis      posterior, 

82. 

fimbria,  171. 

fissura  arcuata  septi,  166. 
formatio  bulbaris,  147. 
fornix,  171,  172. 

relation  to  tsenia  thalami,  221. 
fovea  limbica,  164. 
ganglion,  area  parolfactoria,  165. 

habenulse,  130. 

of  septum,  165. 

ventral,  of  tegmentum,  123. 
gyrus  marginalis,  region  of,  202. 
hemispheres,    cerebral,    161,    162,    165, 

*114. 
interbrain,  ganglia  or  nuclei,  135,  136. 

relation  to  midbrain,  125. 
lobe,  occipital,  163. 
mantle,  145,  146,  160,  161,  177. 

cortex  of,  160. 

structure,  167. 
nerve,  optic,  84,  113. 

spinal  accessory,  85. 

trochlear,  decussation  of,  108. 
nucleus,  auditory,  ventral,  92,  93. 

Deiter's,  99. 

hypoglossal,  87. 

lateralis,  of  midbrain,  121. 
of  vennis  cerebelli,  106. 

magno-cellularis  strati  grisei,  132. 

pneumogastric,  motor,  87. 
oliva  inferior  (?),  98. 

superior  auditory  fibers,  93. 
polus  temporalis,  162. 
septum,  165. 
smell,  sense  of,  176. 
stratum   (layer),  deep  medullary,  302. 
tsenia     thalami,     relation    to     fornix, 
221. 


Vertebrates. 

reptiles,  thalamus  opticus,  132,  135. 

tract    (tractus),    acustico-cerebellaris, 

99. 

cerebello-spinalis,  71. 
cord  to  cerebellum,  101. 
cortico-epistriaticus,  151. 
cortico-habenularis,  130,  131. 
cortico-olfactorius,  151,  166,  217. 
cortico-thalamicus,  135. 
interbrain  to  cerebellum,  101. 
midbrain  to  cerebellum,  101. 
occipito-mesencephalicus,  166. 
strio-thalamicus,  154,  155. 
tecto-thalamicus,  120. 
thalamo-mamillaris,  166. 
tubercle      (tuberculum),      auditory 

(acusticum),  92,  93. 
alligator,  cerebellum,  101,  *57,  105. 
medulla,  cross-section,  82. 
nucleus  nervi  abducentis,  95. 

nervi  facialis,  95. 

thalamus  opticus,  frontal  section,  *82. 
Alligator  luciiis. 

medulla,  closed,  cross-section,  *43. 
nucleus,  auditory,  *49. 

trigeminal,  motor,  *50. 
Alligator  Mississippiensis. 

nucleus,  pneumogastric,  *46. 
Angius  frayilis,  blind-worm. 

intumescentia   lumbalis   et   cervicalis, 

67. 

thalamus  opticus,  frontal  section,  *81. 
armored,  nucleus,  trigeminal,  97. 
Chelone  midas,  see  turtle, 
crocodile,  brain,  *74. 
cerebellum,  101,  *57. 
cord,  section,  *36A. 
interbrain,  125. 
nucleus,  median  thalamic,  132. 
Emys  Europwa,  see  swamp-turtle. 
Emys  lutaria,  see  swamp-turtle. 
Lacerta  agilis,  see  lizard,  also, 
cerebellum,  frontal  section,  *60. 
midbrain,  frontal  section,  *73. 
nerve,  trigeminal,  *51. 
velum  medullare  anticum,  section,  *60. 
lizard,  apparatus,  olfactory,  *100. 
brain,  55,  163,  *113. 

sagittal  section,  *25,  *71,  *76,  127, 

152. 

bulb,  olfactory,  *97. 
cerebellum,  105,  *60. 
cross-section,  *60. 
sagittal  section,  *56,  *57. 
cerebrum,  frontal  section,  *103. 

cortex,  *117. 
chiasma,  section,  *87. 
corpus  striatum,  163. 
decussatio  transversa,  *88. 
epistriatum,  *97. 
fasciculus  retroflexus,  306,  307. 
forebrain,  *97. 
hemisphere,  *114,  *119. 
hypothalamus,  section,  •87. 


418 


INDEX   OF    COMPARATIVE    NEUROLOGY. 


Vertebrates. 

reptiles,  lizard,  intumescentia  lumbalis  et 

cerviealis,  67. 
medulla,  section,  *87. 
midbrain,  frontal  section,  *65,  *73. 

roof,  section,  *66. 
nerve,  trigeminal,  *51. 
Python    Mvittatus,    python,    cerebrum, 

*120. 

snake,  cerebrum,  frontal  section,  *120. 
decapitation-experiment,  70. 
fovea  collateralis,  164. 
nucleus,  median  thalamic,  132. 
swamp-turtle,  brain,  frontal  section,  *99. 
turtle,  brain,  morphology,  163,  164. 
cerebellum,  *57,  105. 
cerebrum,  frontal  section,  *103. 

cortex,  dorsal  plate,  169. 
commissura  grisea  thalami,  132. 
corpus  striatum,  156. 
forebrain,  cross-section,  156. 
fovea  collateralis,  164. 
ganglion,  basal,  forebrain,  156. 

habenula?,  *79. 

hemisphere,  frontal  section,  *118. 
intumescentia   cerviealis   et   lumbalis, 

67. 

mantle,  156. 
mesostriatum,  156. 
nerve,  thoracic,  67. 
nucleus,  median  thalamic,  132. 
tectum  opticum,  98. 
ventricle,  lateral,  156. 
Varanus  griseufs,  see  lizard,  also, 
cerebellum,  105. 

medullary  center,  104. 

sagittal  section,  *56. 

decussatio  transversa,  *88. 

Birds  (Aves). 

apparatus,  olfactory,  174. 

optic,  primary,  175. 
association-bundles   of   cortex   cerebri, 

176,  177. 
body,  olivary,  inferior  (?),  98. 

restiform,  99. 
brain,  11,  12,  164. 

sagittal  section,  *55,  *111. 
capsula  interna,  157. 
centers,  optic,  287. 
cerebellum,  *57,  105. 

fibrfe  arcuatee  externse,  108. 

peduncles,  107. 
inferior,  99. 

plate,  cells  of,  104. 

ventricle,  101. 

worm,  102. 
cerebrum, 

connection    with    tectum    mesence- 

phali,  114. 

chiasma,  optic,  139,  140. 
cochlea,  91. 

column  of  Stilling-Clarke,  66. 
commissura  grisea  thalami,  132. 
corona  radiata,  176. 


Vertebrates. 

birds,  corpus  geniculatum,  133. 

quadrigeminum,  308. 

striatum,  155,  156,  157. 
cortex      cerebri,      association-bundles, 

176,  177. 

dendrites,  ganglion-cells,  73. 
epiphysis,  127,  128,  130. 
fibers,  arciform,  external,  99. 
fillet,  71,  124. 
forebrain,  compared  with  turtle's,  156. 

frontal  secuon,  *105. 
fornix,  171,  172. 
fossa  (sinus)  rhomboidalis,  73. 
fovea  collateralis,  164. 
ganglion,  hypothalamic,  132. 

of  thalamus,  132,  134. 

ventrale  tegmenti,  123. 
globus  pallidus,  157. 
hemispheres,  11,  12,  162. 
laver  (stratum),  deep  medullary,  118. 
lobe,  occipital,  163,  175. 

optic,  113. 
lobus  cerebellaris  nervi  acustici,  105. 

trigemini,  105. 

mantle,   145,   146,   155,   156,   160,   161, 
177. 

structure,  167. 
midbrain,  base,  121. 

connection  with  cerebrum,  114. 

roof,  113. 
nerve,  auditory,  91-93. 

cranial,  number,  59. 

optic,  84,  113,  139. 

spinal  accessory,  85. 
nucleus,  auditory,  91,  93. 

caudatus,  157. 

cerebellar,  105. 

columns,   posterior,  of  medulla,   79, 
81. 

Deiter's  99,  108. 

hypoglossal,  87. 

lateralis  mesencephali,  121. 
vermis,  106. 

magno-cellularis  strati  grisei,  132 

pneumogastric,  86,  87. 

rotundus,  interbrain,  132. 

thalami.  134. 

trigeminal,  frontal,  97. 
oliva  inferior  (?),  98. 
superior  auditory  fibers,  93. 
putamen,   157. 
septum,  165. 
stratum   (layer),  deep  medullarv.  30?. 

302. 

tectum  mesencephali,  114. 
thalamus  opticus.  132. 

ganglia  of  nuclei,  134. 
tract  (tractus). 

auditory  cerebellar,  99. 

cerebello-spinalis,  71. 

cord  to  cerebellum,  101. 

cortico-habenularis,  130,  131. 

cortico-olfactorius,  151. 

cortico-thalamicus,  135. 


IXDEX   OF    COMPARATIVE   NEUROLOGY. 


419 


Vertebrates. 

birds,  tract  from  Deiter's  nucleus,  108. 
from  putamen,  157. 
interbrain  to  cerebellum,  101. 
midbrain  to  cerebellum,  101. 
occipito-frontalis,  177. 
occipito-mesencephalicus,  174,  175. 
olfactory,  fibers,  149. 
olfactory,  of  septum,  166. 
optic,  midbrain,  124. 
septo-mesencephalicus,  166,  175. 
strio-thalamicus,    155. 
tecto-thalamicus,    120. 
thalamo-mamillaris,  132. 
tuberculum  acusticum,  auditory  tuber- 
cle, 93. 

ventriculus  cerebelli,  101. 
vermis  cerebelli;  102. 
vision,  physiology  of,  176. 
chicken,  brain,  sagittal  section,  *21,  *72, 

*115. 

cerebellum,  sagittal  section,  *61. 
peduncles,  inferior,  *61. 

superior,  *61. 
cord,  spinal,  section,  *33. 

central  fibers,  87. 

fasciculus  longitudinalis  lateralis,  72. 
duck,  decapitation-experiment,  70. 
ostrich,  cord,  section,  *36#. 
owl.  decussation,  optic,  140,  141. 
parrot,  brain,  frontal  section,  *104. 
pigeon,  brain,  sagittal  section,  *121. 
association-bundles,      cortex      cerebri, 

177. 

interbrain,  *83. 

thalamus,  sagittal  section,  *84. 
tractus  occipito-mesencephalicus,  174. 
sparrow,      medulla,      glosso-pharyngeal, 
*47. 

Mammals  (Mammalia). 
ansa  lentiformis,  256. 
apparatus,    olfactory,    150,    208,    211, 

226. 
aqueduct  of  Sylvius,  113. 

matter,  gray,  121. 

association-bundles,      cortex      cerebri, 
176,  177. 

nucleus  caudatus,  257,  258. 
body,  olivary,  cerebellar,  106. 

inferior,  98. 

restiform.  99. 
brain,  154,  208-226. 

sagittal  section.  *112. 
capsula  interna,  155,  157,  178. 
center,  olfactory,  209. 
cerebellum,  102,  104,  *57,  105,  110,  326. 

fibers,  arciform,  external,  108. 

oliva  cerebelli,  106. 

peduncles,  107,  108. 
inferior,  99. 
middle.  108. 

plate,  cells,  104. 

ventricle,  101. 
cerebrum,  145. 


Vertebrates. 

mammals,  cerebrum,  peduncles,  124. 

relation  to  cerebellum,  110,  145. 

tectum  mesencephali,  114. 
chiasma  optica,  139,  140. 
claustrum,  169. 
cochlea,  91. 
commissure,   anterior,   cerebrum,   216. 

grisea  thalami,  132. 

mollis,  132. 

of  mantle,  172. 

posterior,  295. 
control,  sensory,  44. 
cord,  spinal,  effect  of  removal,  75. 

column  of  Stilling-Clarke,  66. 
cornu  Ammonis,  170,  171. 
corona  radiata,  135. 
corpus  callosum,  160,  172,  200,  218. 

quadrigeminum  anterius,  284,  308. 
peduncle,  143. 
posterius,  114,  284. 

striatum,  156,  157. 

subthalamicum,  123. 

trapezoides,  93. 
cortex  cerebri,  176,  209. 

association-bundles,  176,  177. 

fibers,  155. 

olfactory,  152,  169,  170,  172. 

physiology,  173,  209. 
•  radiation,  210. 

removal,  effect,  208. 

section,  *152. 

surface,  173. 

decussation,   anterior,  of  spinal  cord, 
70. 

optic,  140-142. 

dendrites  of  gray  ganglion-cells,  73. 
epiphysis,  127,  128,  130. 
epistriatum  (?),  215. 
epithelium,  central  canal,  16. 
fasciculus  longitudinalis  posterior,  71, 

82,  295. 

fibrae  arciformes  (arcuatse)  internee,  99. 
fillet,  124. 
fissure,  inner  marginal,  166. 

limbica,  200. 

Sylvius,  variations,  221. 

transitory,  203. 

forebrain,  frontal  section,  *105. 
fornix,  171.  172,  200. 
fovea  collateralis,  164. 
ganglion  habenula;,  129. 

hypothalami,  132. 

thalami,  132. 

ganglion-cells,  anterior  horn,  67. 
germ-cells,  16. 
globus  pallidus,  157. 

fyri,  179. 
emispheres,  50,  51,  162,  165. 
hypophysis,  128. 
impulses,  transmission  of,  23. 
interbrain,  nuclei,  135,  136. 
lobe  frontal,  178. 
occipital,  163,  175. 
olfactory,  146. 


420 


IXDEX    OF    COMPAKATIVE   NEUROLOGY. 


Vertebrates. 

mammals,  lobus  cerebellaris  acustici,  105. 

cerebellaris  trigemini,  105. 
mantle,   145,   146,   153,   155,   160,   161, 
172,  177,  178. 

structure,  167. 
midbrain,   connection   with   cerebrum, 

114. 

muscles,  innervation,  37. 
nerve,  auditory,  91,  «2,  93. 

cranial,  number,  59. 

optic,  84,  113,  143,  285,  286. 

sensory,  deep  centers,  176. 

spinal  "accessory,  85. 
neuraxons,  20. 
nucleus  arciformis,  98. 

auditory,  91,  93. 

caudatus,  157,  257,  258. 

cerebellar,  105. 

column,  posterior,  medulla,  79,  81. 

Deiter's  93,  108. 

dentatus  olivae  cerebelli,  106. 
fasciculi  longitudinalis  posterioris,  305. 

lateralis  vermis,  106. 

nerves,  cranial,  terminal,  84. 

pneumogastric,  86. 

pnetectalis  (?),  114,  136. 

roof  of  midbrain   (?),  120. 

thalami,  136. 
oliva  inferior,  98,  381.  * 

superior,  388,  389. 
paths,  motor,  37. 
pes  cerebri,  211. 

polus  frontalis  et  occipitalis,  163. 
psalterium,  172. 
pulvinar,  287. 
putamen,  157. 
radix  mesencephalica  nervi  trigemini, 

97,  120. 

rhinencephalon,  216. 
roots,  olfactory,  215. 
septum  pellucidum,  165. 
sheath,  medullary,  30. 
substantia  nigra,  123. 
sulci  cerebri,  164. 
tectum  mesencephali,  114. 
thalamus  opticus,  132. 
tract  (tractus),  bulbar,  efferent,  149. 

cerebello-olivaris,  108,  326.     • 

cerebello-spinalis,   71,  311. 

cerellum  to  cranial  sensory  nerves, 
327. 

cerebrum  to  cerebellum,  101. 
to  medulla,  99. 

cord  to  cerebellum,  101. 

cortex  to  corpus  geniculatum,  136. 

cortical,  145. 

cortico-habenularis,   130,   131. 

cortico-olfactorius,  151. 

cortico-spinalis,  72,  83. 

cortico-tnalamicus,  135. 

Deiter's  nucleus,  108. 

habenulo-peduncularis,  276. 

interbrain  to  cerebellum,  101. 
to  pons  and  cord,  124. 


Vertebrates. 

mammals,  tract,  occipito-mesencephalicus, 

174. 

olfactorius  septi,  166. 
optic,  124,  287. 

septo-mesencephalicus    (?),   166. 
spinal,  71. 

strio-thalamicus,  136,  144,  155,  157. 
tecto-thalamicus,  120. 
thalamo-bulbaris  et  spinalis,  136. 
thalamo-mamillaris,   132. 
vago-cerebellar,  86. 

tuberculum   acusticum    (auditory   tu- 
bercle), 93.  • 
ventriculus  cerebelli,  101. 
vision,  physiology  of,  176. 
ape,  convolutions,  205. 
corpus  callosum,  173. 
cortex,    relation    to    animal    activity, 

209. 

decussation,  optic,  140,  141. 
fissura  perpendicularis  externa,  203. 

simian,  198. 
gyri,  179,  205. 
frontal,  194. 
lobe,  frontal,  210. 
medulla,  *246. 
tract,  pyramidal,  346. 

crossed,  72. 
trapezium,  *246. 
apes,  anthropoid, 
brain,  194. 

literature  of  gyri,  223. 
convolutions,  205. 
lobe,  frontal,  210. 
mantle,  210. 
aquatic,  apparatus,  olfactory,  211. 

cornu  Ammonis,  171. 
anosmatic,  211. 

lobe,  limbic,  216. 
armadillo. 

apparatus,  olfactory,  *139. 
brain,  *  139,  211,  *140. 

olfactory,  212. 
cortex,  209. 

lobes,  olfactory,  209,  212. 
bear,  brain,  *145,  222. 
fissure,  central,  221,  222. 
lobe,  frontal,  *145,  222. 
burrowers,  tract,  pyramidal,  346. 
calf,  brain,  base,  211. 
olfactory,  212. 
sagittaf  section,  *143. 
corpus  trapezoides,  311. 
lobus  limbicus,  *143. 
carnirorn,  brain-surface,  literature,  223. 
cat,  brain,  sagittal  section,  *19. 
corpus  geniculatum  laterale,  *184. 

quadrigeminum   anterius,  287. 
cortex  cerebri,  *149. 
fibers,  oculo-motor,  55. 

optic,  287. 

zone,  antero-lateral  mixed,  of  cord,  350. 
cow,  brain,  surface,  223. 

commissure,  posterior,  of  cord,  358. 


IXDEX    OF    COMPAKATIVE    NEUROLOGY. 


421 


Vertebrates. 

mammals,  Dasypits  villosus,  see  armadillo, 
dog,  brain,  *147. 

frontal  section,  *169,  *191. 
olfactory,  212. 
surface,"  223. 
cingulum,  239,  240. 
commissure  of  Meynert,  260. 

posterior,  of  cord,  358. 
cord,  spinal,  lateral  column,  *220. 
cortex,  removal  of,  257. 
fasciculus  fronto-occipitalis,  242. 
ganglion  interpedunculare,  306. 
gyrus  hippo6ampi,  235. 
interbrain,  frontal  section,  *176,  *177. 
labyrinth,  removal,  44. 
lobe,  frontal,  *147. 
mantle,  removal,  155. 
regio  subthalamica,  273,  274. 
stratum  intermedium,  274. 
substantia  reticularis  pontis,  315. 
tapetum,  242. 
thalamus,   section,  frontal,   *169,  263, 

*176,  *177. 

tracts,  from  corpus  striatum,  257. 
cortico-spinalis,  *35A. 
crossed  pyramidal,  72. 
olfactory,  220,  221. 
dolphin,  lobe,  olfactory   (?),  216. 
ecJtifhifi.  gyri,  179. 
elephant,  cortex,  facial  center,  210. 
guinea-pig,  tract,  crossed  pyramidal,  72. 
gyrencephalic  mammals,  179. 
ha  pale,  see  ape. 
horse,  brain,  223. 

cord,  74. 

insectivora,  corpus  callosum,  173. 
lemurs,  surface  of  brain,  literature,  223. 
lissencephalic  mammals,  179. 
lower  mammals,  tract,  pyramidal,  346. 
man,  apparatus,  olfactory,  211. 
area,  olfactory,  282. 
brain,  sagittal  section,  embryonic,  *20. 

surface,  embryonic,  *23. 
cerebrum,  178. 

frontal  section,  *22. 
commissure,  anterior,  242. 
convolutions,  205. 
cord,  spinal,  posterior  roots,  354. 
cornu  Ammonis,  215. 
corpus  callosum,  173. 

geniculatum  mediale,  133. 
quadrigeminum  anterius,  287. 
cortex  cerebri,  208,  209. 

association-bundles,  176,  177. 
decussation,  optic,  140,  141. 
forebrain,  209. 
fornix  longus,  220. 
ganglion-cell,  post-embryonic  increase, 

55. 
gyrus  callosus,  200. 

fornicatus,  216. 
lobe,  frontal,  178. 

limbic,  216. 
mantle,  146,  178,  210. 


Vertebrates. 

mammals,     man,     nucleus,     oculo-motor, 

303. 

pulvinar,  259. 
tract  ( tractus ). 

cortico-olfactorius  septi    (?),  217. 
.      crossed  pyramidal,  72,  *35B. 
direct  pyramidal,  72,  *35B. 
occipito-mesencephalicus,  174. 
marsupials  (Marftupialia). 
apparatus,  olfactory,  224. 
brain,  177.  *123. 
corpus  callosum   (?),  211. 
fissures.  203. 
mantle,  177. 
tract  (tractus). 

cortico-olfactorius  septi,  217. 
pyramidal,  346. 
mole,    corpus    quadrigeminum    anterius. 

308. 

Monodon  monoceros,  see  narwhal, 
monotremes  (monotremata),  see  echidna 

and  ornitliorhynchvs. 
apparatus,  olfactory,  224. 
corpus  callosum  ('!),  211. 
gyri,   179. 
mouse,    cerebrum,    white    medulla,    178, 

247. 

collaterals  of  white  medulla,  247. 
cord,  spinal,  *34. 
hair,  innervation  of,  *17. 
hemisphere,  *119. 
tract,  crossed  pyramidal,  72. 
narwhal,  brain,  *146. 

convolutions,  223. 

nniitJtorJiynchus.  lissencephalic,  179. 
osmatic  mammals,  211. 
bundle,  olfactory,  283. 
cornu  Ammonis,  242. 
corpus  callosum,  242. 

mamillare,  274. 
fimbria,  218. 
fornix,  218. 
lobus  hippocampi,  215. 

limbica,  216. 
psalterium,  218. 
roots,  olfactory,  282,  283. 
ox,  cord,  spinal,  74. 
primates,  apparatus,  olfactory,  282. 
association-centers,  brain,  210. 
corpus  mamillare,  274. 
fasciculus       longitudinalis       inferior, 

240. 

fissures,  203. 
gyri,  179. 

lobus  olfactorius,  282. 
pulvinar,  297. 
rabbit,  brain,  sagittal  section,  144. 

olfactory,  212. 
cingulum,*  239.  240. 
(jornu  Ammonis.  section,  *9. 
corpus  quadrigeminum   anterius,  285- 

cortex,  areas,  *149. 
decapitation-experiment,  70. 


422 


IXDEX  OF  COMPARATIVE  NEUROLOGY. 


Vertebrates. 

mammals,   rabbit,   glandula   pinealis,   276. 
nucleus  magno-cellularis,  260. 

thalami,  260. 

tract,  optic,  fibers,  285-287. 
trigeminal,  central,  396. 
trigemenal,  cortical,  408. 
rhinoceros,  cortex,  facial  center,  210. 
rodents  (Rodentla),  cornu  Ammonis,  171. 


Vertebrates. 

mammals,  rodents,  corpus  callosum,  173. 
simians,  convolutions,  198. 
tapir,  cortex,  facial  center,  210. 
tfiylacinus,  see  marsupials, 
ungulates,  brain- surface,  literature,  223. 
whales,  brain-surface,  literature,  223. 
corpus  quadrigeminum  posterius,  285. 
nucleus  nervi  acustici,  285. 


GENERAL  INDEX. 


Only  nouns  are  indexed.     The  figures  immediately  preceded  by  an  asterisk  (*) 
refer  to  illustrations. 


Abducens,  see  nerve,  abducent. 
Abduction  of  eye,  309. 
Abductors,  of  thigh,  337. 
Abscess  of  brain,  329,  330. 

of  cerebellum,  329. 

Accessorius,  see  nerve,  spinal  accessory. 
Activity,  cerebral,  72. 

cord,  spinal,  71. 

Acts,  voluntary,  cortical  centers,  227. 
Acusticus,  see  nerve,  auditory. 
Adductors  of  thigh,  337. 
Afterbrain,  *182,  *236. 
Age,  as  affecting  structure  of  cortex,  233. 
Ala  cinerea,  *182,  *236,  374. 

lobuli  centralis,  316. 
Alcohol,  fixation-method,  24. 
Alveus,  *125,  *144,  *154,  236,  *177. 
Amblyopia,  269. 

Ampulla,  sensory  epithelium,  390. 
Anarthria,  403,  405. 

Anatomy,  comparative,  of  brain,  10,  11,  12. 
centers,  optic,  287. 
convolutions,  210. 

Ansa  lentiformis,  256,  257,  *167,  *168,  *169, 
262,  263,  267,  269,  *174,  *176, 
274,  *177,  *178,  277,  280,  *191; 
see  also  tractus  strio-thalam- 
icus. 

peduncularis,  *141,  263,  274. 
Anus,  center,  cortical,  *149. 
Aphasia,  253. 

Aphonia,  lesions  of  medulla,  405. 
Apoplexy,  symptomatology,  407. 
pars  corticalis,  *101. 
physiology,  158. 
primates,  282. 

relation  to  commissura  anterior,  242. 
conus  frontalis  pallii,  169. 
cornu  Ammonis,  170.  171. 
corpus  striatum,  145. 
ganglion  habenulse,  131. 
mantle  or  pallium,  211. 
tenia  thalami,  188,  *169. 
Apparatus,  olfactory.  56,   146-153,   162,   165- 
167,  174,  209,  211,  213,  216,  218, 
221,  283. 

of  armadillo,  *139. 
center,  cortical,  152,  207. 
gyrus  rectus,  201. 
subcallosus,  201. 


Apparatus,  olfactory,  literature,  224. 
lobus  pyriformis,  213. 
mammals,  208-226. 

schema,  *98,  *100,  *101,  *144,  173,  242. 
tractus  cortico-olfactorius  septi,  201,  217. 

stria-olfactorius,  *141,  *143,  *144. 
optic,  primary,  175. 
sensory,  Coelenterates,  39. 
Aqueduct  of  Sylvius,  *21,  113,  *66,  121,  124, 
144,  *165,  *185,  289,  *186,  »187, 
295,  *191,  301,  *197,  *199,  308. 
310,  312,  313,  315,  399. 
floor- nuclei,  *196,  303. 
relation  to  bundle,  tegmental,  275. 
commissura  posterior,  295. 
nucleus  fasciculi  longitudinalis  posteri- 

oris,  305. 

nervi  oculo-motorii,  303,  304. 
nervi  trigemini,  439. 
radix  mesencephalica  nervi  trigemini,  97, 

394,  399. 

stratum   (layer),  deep  medullary,  301. 
ventriculus  quartus,  324. 
substance  (matter),  central  gray,  278,  305, 

308,  377. 

Arbor  vite,  318,  *206,  319. 
Arborescence    (arborization),   *16,   359;     see 

also  ramification, 
cells  of  Clarke's  column,  354. 

cortex  cerebri,  231. 
fibers,  optic,  *184,  287. 
fibrils,  pyramidal,  351. 
ganglion-cells  of  cord,  341. 
neuraxons,  22. 
olfactory,  213. 
retinal,  287. 
Arch,  branchial,  47. 
Area,  of  fornix,  200. 
auditory,  409. 
Brocse,  266. 

cortical,  reptiles,  168,  169. 
hypoglossal,  406. 
trigeminal,  408. 
lateral,  of  mantle,  159. 
motor,  208. 

olfactory,    *76,    146,    147,    149,    *100,    152, 
*103,    '113,    »114.    '118,    "123, 
*135,  215,   *172,  266;     see  also 
spatium  olfactorium. 
cortex  cerebri,  213,  221. 

(423) 


424 


GENERAL    INDEX. 


Area,  olfactory,  fibers,  217. 

relation  to  lobus  supracallosus,  216. 
substantia  perforata  anterior,  282. 
taenia  thalami,  220,  306. 
parolfactoria,  *76,  165,  *118. 
projection,  cortical,  *148. 
psychomotor,  136. 
Arm,  see  also  brachium. 
center,  cortex  cerebri,  *148. 
cerebellar,  see  peduncles, 
commissural,  319. 

corpus  quadrigeminum  anterius,  *192,  298. 
pons,  315. 

Arteriosclerosis,  cerebellum,  329. 
Association  of  cortical  centers  by  exercise, 

32. 

of  nerve-fibers,  29. 

Association-area,  cortex  cerebri,  226. 
Association-bundles,  254. 
center,  olfactory,  152. 
cord,  spinal,  345.' 
cortex  cerebri,  176,  177. 
fronto-occipital,  258,  265,  267. 
interlobular,  240. 
nucleus  caudatus,  240,  257,  258. 
polus  frontalis,  264. 
Association-cells,  29. 

cornu  Ammonia,  *9,  236. 
schema,  *11. 
Association-center,  cortex   cerebri,   173,  210, 

246,  247. 
medulla,  94. 

Association-fibers,  cerebellum,  110. 
cord,  spinal,  358. 

commissure,  anterior,  358. 
cortex  cerebri,  173,  237-239,  266,  267. 
long,  265. 

short,  265,  290,  294. 
mantle,  246. 
medulla,  80,  98,  384. 
schema,  *156. 

Association-field,  medulla,  366,  384,  396. 
Association-net,  cerebellum,  110. 
Association-pathways,    cortex    cerebri,    233, 

240. 

formation  of,  233,  234. 
Association-system,  cord,  spinal,  354. 
cortex  cerebri,  264. 
medulla,  98. 
Association-tracts,   cortex   cerebri,   246,   265, 

277,  296. 

midbrain,  intratectal,  114. 
Astrocytes,  cortex  cerebri,  237. 
Ataxia,  cerebellar,  330,  33 1. 
cerebral,  331. 

lesion  of  corpus  quadrigeminum,  331. 
tabes  dorsalis,  357. 
Athetosis,  lesion  of  thalamus,  270. 
Atrophy,  muscular  amyotrophic  lateral  scle- 
rosis, 361,  362. 
cord,  lesions,  360,  362. 
medulla,  lesions,  402,  405,  407. 
poliomyelitis  anterior  acuta,  362. 
optic,  309. 
Atrophy-method  of  investigation,  9. 


Auris,  center,  *149. 

Axis-cylinder,  *4,  20-23,  25,  30,  37,  *15,  *16, 

69-71. 

bundle,  tegmental,  275. 
cells  of  Gasserian  ganglion,  409. 
olivary,  380. 
spinal  ganglia,  341. 
substantia  gelatinosa  of  Rolando,  341. 
collaterals,  *220. 
degeneration,  7. 
ganglion-cells,  6,  341,  342,  *227,  351,  355, 

405. 

germ-cells,  15. 
nerves,  motor,  338,  339. 

sensory,  62,  143. 
staining  methods,  5. 
structure,  *10. 
tracts,  pyramidal,  351. 

sensory,  of  cord,  66. 
Axone,  22,  37,  40,  *15. 

Base,  of  brain,  *154,  *180. 
interbrain,  128. 
lesions,  405. 
midbrain    (mesencephalon),   56,    124,   *86, 

*95. 

Bergmann-Deiter  fibers,   329. 
Biceps,  center,  in  cord,  336. 
Bladder,  innervation,  42. 
Blood-supply,  regulation,  43. 
Blood-vessels,  of  cord,  343. 

nerve-endings,  sensory,  41. 
Body,  see  also  corpus, 
corpus  callosum,  197. 
geniculate,  external,  *70. 

lateral,  optic  fibers,  287. 
Nissl's,  24. 
olivary,  3,  99. 
accessory,  *243. 

inferior," 98,  *183.  326,  366,  373,  374,  379. 
superior,  *46,  *48,  93,  *53,  96,  98,  108. 
pineal,  189;    see  also  gland  and  epiphysis. 
quadrigeminal,  308. 

oblique  section,  300. 
anterior,  136,  297,  301,  399,  400. 
pedicle,  *191. 

relation  to  cerebellar  peduncle,  326. 
section,  frontal,  *198,  *199. 
posterior,  lateral  fillet,  313. 

nucleus  ruber,  299. 
restiform,  99,  *234,  313,  382,  384. 
Brachialis  anticus,  spinal  center,  336. 
Brachium,  see  also  arm. 

relation  to  optic  tract,  285. 
anterius,  *61,  285,  *183,  *192,  *193. 
cerebelli  anterius,  *252,  399,  400. 
conjunctivum,  381. 
anterius,  107. 
posterius,  *247. 
pontis    (middle   cerebellar  peduncle),  311, 

*205,  315,  324,  326. 
lesion,  329. 

posterius,  285,  *183,  *194,  *199. 
Brain,  armadillo,  *139. 

base,  263,  280,  *180,  283,  302. 


GENERAL   INDEX. 


425 


Brain,  base,  lesion,  283. 

convolutions.  *135,  203,  *138,  204,  207. 

Cuvier's,  207. 

development,  47-61,  206. 

dog,  *147,  223. 

Gambetta's,  206. 

Gauss's,  205. 

growth,  55. 

hardening-method,  264. 

human  embryonic,  146,  *128. 

lizard,  *113. 

mammals,  164,  208-226. 

mantle-fibers,  296. 

maturation,  55. 

morphology,  183-207. 

olfactory,  211,  212. 

Rubinstein's,  207. 

section,  frontal,  *127,  250,  *167-*170,  264, 

*171-*175,  *178,  *185-*189. 
horizontal,  *125,  *160. 
sagittal,  *109. 
bird,  '111. 
chicken,  *115. 
human  embryo,  *20,  *181. 
kitten,  *19. 
mammal,  *112. 
rabbit,  *144. 
ray,  *122. 
reptile,  *110. 
selachian,  *108. 
sturgeon,  *18,  49. 
teleost,  *107. 
size,  206. 
view,  basal,  armadillo,  211. 

calf,  *141. 

lateral,  man,  '130,  *131. 
weight.  206,  207. 
Brain-cell,  24. 

Brain-centers,  primary,  173. 
Brain-sand,  276. 
Branch,  arbor  vitse,  319. 
fissure  of  Sylvius,  194. 
masseteric.  of  trigeminal,  85,  95. 
nerve,  auditory,  ascending,  92. 
cochlear,  *16. 
descending,  92. 
trigeminal,  sensory,  95. 
nerve-root,  posterior  spinal,  352. 
ascending,  62,  352. 
descending,  62,  353. 
neuraxon,  21. 
neurite,  sensory,  69. 
Bristle-projections,  epithelial  cells  of  canal, 

16. 

Bulb,  see  medulla. 

Bulbus   (bulb)   olfactorius.  *25,  58,  *96,  *97, 
147,   148,   *98,   *110,   *141,  212, 
213,  *142,  *144,  220,  *180,  282. 
cortex,  213,  236. 
medulla,  215. 
neuraxons,  215. 
radiations,  215. 
relation  to  olfactory  lobe  and  field,  217, 

218. 
section,  sagittal,  *94. 


Bulbus    olfactorius,     structure,     213,     *142. 

215. 

tractus  bulbo-corticalis,  150,  215. 
bulbo-epistriaticus,  169. 
olfactorius,  282. 
ventricular  epithelium,  214. 
Bundle,  see  also  fasciculus. 

association,  of  nucleus  caudatus,  257,  258, 

*169,  '176,  *177. 
polus  frontalis,  264. 
basal,   of   forebrain,    154,   256,    *176;     see 

ansa  lentiformis. 
cord,  spinal,  '227. 
corona  radiata,  246,  272. 
crusta  to  tegmentum,  406. 
fornix,  186. 
Gowers's,  328. 
Gratiolet,  288. 

interolivary,  368;    see  also  fillet,  lemniscus. 
lateral,  of  pes  pedunculi,  290. 
longitudinal,  inferior,  292. 
lateral,  midbrain,  121. 
posterior,  71,  *42,  82,  *43,  '44,  93,  *51- 

*54,  99,  *65,  '67,  117,  122,  123, 

*73,  124,  *76,  *83.  '175,  '177, 

'179,  278,  *191,  '198,  392,  397. 
Meynert,  306. 
midbrain,  deep  medullary  stratum  (layer), 

*68. 

nerve,  optic,  *71. 
olfactory,   169,   *141.  217,  218,   '144,  220, 

*169,  274,  283. 
tegmental,  144,  '176. 
tegmento-mamillary,  274,  '177,  277. 
Vicq   d'Azyr,   132,' '144,   '158,   '169,   268, 

*176,   274,   277,   280;     see   also 

tractus  thalamo-mamillaris. 

Calcar  avis,  198. 

Canal,  central,  16,  56,  62,  63,  *33,  '190,  '216. 
epithelium,  *5,  344. 

medulla,  57,  75,  78,  363,  368,  372,  374,  376. 
neural,  15,  16,  36. 

sensory,  aquatic  vertebrates,  59.  60,  97. 
Capsula  externa,   190,  216,  250,  '171,  '172, 

266,  '176,  277,  406. 

interna.  54,  144,  155,  157,  178,  189,  '127, 
190,  242,  245,  248-257.  '160, 
*162-*165,  259,  *168-*177.  263, 
265-267,  269-272,  274,  276-278, 
'179,  280,  285,  '183,  288,  '185, 
291,  294,  '193,  344,  '221,  366, 
405-409. 

medullary,  of  corpus  mamillare,  '178.  277. 
of  nucleus,  anterior  thalami,  '169,  269. 

ruber,  278. 

Caput  of  cornu  posterius,  '234.  374. 
fornicis,  '144. 

nuclei  caudati.  189,  257,  '171. 
I  Corpus,  center,  '148. 
j  Cavity,  central,  of  interbrain,  55,  *25,   126, 

127. 

cerebellar,  *21. 
cerebral,  *21,  53,  162. 
cranial,  52,  126. 


426 


GENERAL    INDEX. 


Cavity,  medulla,  *21. 

preoral,  sturgeon,  129. 
Cell,  bipolar,  *15. 

Clarke's  column,  *219,  350,  354,  357. 

claustrum,  250. 

commissural,  69,  70,  71,  80,  84,  365,  366, 

384. 

cornu  Ammonis,  *9,  29. 
cortical,  24,  167,  168,  231,  235,  298. 
Deiter's,  17,  93,  237,  328. 
"dorsal"  cyclostomes,  73. 
epithelial,  neural  canal,  15,  16. 
fibers  of  Mauthner,  94. 
fusiform,  231. 
ganglion,  Gasserian,  394. 

of  cord,  *15,  332-334,  340,  346,  347. 
ganglionic,  of  ear,  40,  92. 

of  pons,  311,  407. 
'•germ-cells,"  *15. 
"hair-cells,"  crista  acustica,  40. 
hypophysis,  281. 
individuality  of,  320. 
labyrinth,  390. 

layer,  granular  cerebellar,  320. 
lobes,  electric,  89. 
locus  creruleus,  399. 
mitral,  olfactory  cortex,  *142. 
motor,  ganglionic,  *6,  23,  *37,  79,  84,  87, 
337,   339,  340,   *218,   *227,  351, 
355,  357,  362,  405,  406. 
mucous  membrane,  olfactory,  213. 
neuroglia,  *4,  214. 
olfactory,  *16,  147,  213. 
pigmented,  nerve-reticulum,  *17. 
polygonal,  228,  234. 
Purkinje's,  *47,  104,  *60,  110,  319-321,  *208, 

328,  380. 
pyramidal,  *9,  29,  150,  227,  228,  231,  234, 

236. 

retina,  40,  287. 
sensory,  ganglionic,  15,  22,  39,  40,  59,  62, 

339-341,  *219,  355-358. 
substantia    gelatinosa    of    Rolando,    341, 

*219. 

nigra,  272,  299. 
sympathetic,  of  cord,  333. 
system,  peripheral  nervous,  37. 
types,  20,  21,  62. 

Cellulse  commissurales,  *33,  69,  80. 
Center,  cerebellum,  muscle-tonus,  110. 
cord,  spinal,  brachial  plexus,  340. 
nerves,  motor,  351. 
reflex,  336,  337. 
skin,  336,  337. 
cortical,  208,  *148,  *149. 

association,  173,  210,  246,  247. 
extremities,  *258. 
memory-pictures,  173. 
motor,  44,  208,  *148,  *149,  *258. 
nerves,  cranial, 

auditory,  *148,  *149,  *246. 

facial,  210,  *148,  *149,  225,  251,  267, 

*258. 

hypoglossal,  *148,  *149,  225,  251,  267, 
377,   406. 


Center,  cortical,  nerves,  olfactory,   151,   152, 

171,  174,  209,  *149,  220,  246. 
optic,  136,  175,  176,  *148,  245,  246,  287, 

288,  294,  *190,  410. 
sense,  muscular,  269. 
sensibility,  225,  226. 
sensory,  176,  208,  246,  247. 
smell,  171,  218. 

speech  (sermo),  *148,  240,  247,  267. 
taste,  *148,  378. 
medullary,  association,  94. 
co-ordination,  100. 
equilibrium,  94. 
Centrum  ovale,  lesion,  403. 

semiovale,  184,  *124,  *127,  210,  237,  *162, 

252,  *164,  *176. 

Cerebellum,  5,  *18.  50,  *20,  *25,  *37-*39,  *44, 
101-111,  *55,  *63,  *71,  *74,  *76, 
*80,  *83,  134,  *86,  *88,  *95,  106- 
110,  112-115,  122,  187,  *144,  *182, 
293,  *190,  299,  *200,  315-331, 
*236,  *237,  *241,  *243,  *244,  388, 
399. 

association-fibers,  110. 
ataxia,  330. 
cell-plate,  103. 
center  of  co-ordination,  110. 
medullary,  105. 
muscle-tonus,  110. 
connections,  110,  325. 
cerebral.  145,  315,  336. 
cord,  spinal,  66,  71,  110,  315. 
corona  radiata,  178. 
corpus  opticum,  56. 
fibi-ge  arcuate,  83. 
hypothalamus,  134. 
interbrain,  110. 
medulla,  110,  315. 
midbrain,  110,  122. 
nerve,  auditory,  92,  93. 

vestibular,  409. 

nucleus,  auditory,  91,  105,  391. 
Bechterew,  391. 
ruber  tegmenti,  li>7. 
sensory  pneumogastric,  86. 
trigeminal,  98,  105. 
oliva  inferior,  98. 

superior,  409. 
peg  pedunculi,  315. 
pons,  280,  311,  315,  385. 
tegmentum,  315. 
tela  chorioidea  inferior,  *37. 
thalamus,  315. 
co-ordination,  104,  105. 
corpus,  see  corpus, 
cortex,  see  cortex, 
development,  101,  102,  310. 
Dipnoi,  101. 
disease  of,  329,  330. 
embolus,  322. 
facies  caudalis,  *56. 

frontalis,  *56. 

fibrse  semicirculares,  *209,  210. 
fissures,  see  fissures, 
formatio  cerebelli,  75. 


GENERAL    INDEX. 


427 


Cerebellum,  function,  102,  104,  105,  110. 
hemispheres,  102,  211. 
histology,  103,  320-322,  329. 
lamina  "(layer)  granulosa,  *47,  104,  *60. 
medullaris,  104,  320,  321. 
molecularis,  *47,  *60,  108,  110. 
literature,  329. 
lobes,  315-318;    see  lobes, 
nucleus,  see  nucleus, 
ontogeny,  103. 
peduncles,  see  peduncles, 
phylogeny,  102,  103. 
sections,  250. 

frontal,  324.  *210,  *212. 
horizontal,  *209. 
sagittal,  *61,  182,  318,  *206. 
substance  (matter),  gray,  322,  323. 

white,  318,  319. 
surface,  104,  105,  307,  315,  316,  *203,  '204, 

329. 

swimmers,  101,  102. 
tumor,  symptoms,  330,  331. 
types,  105. 

valvula,  *39,  105,  107,  *68,  *85,  *86,  *95. 
velum,  see  velum, 
vermis,  102,  105,  108;    see  vermis. 
zona  granulosa,  320,  *207,  328,  329. 

molecularis,  110,  320,  *207. 
zone  of  decussation,  *210. 
Cerebrum,  145-179. 

apparatus,  olfactory,  146-153. 
basis,  *154,  280. 
brain-centers,  primary,  173. 
commissures,  see  commissures, 
convolutions,  191-207;    see  also  gyrus. 
corpus  striatum,  153-158;    see  also  corpus 

striatum. 
cortex,   167-174,  227-234;    see  also  cortex, 

cerebral. 

development,  47-61. 
fissures,  191-207;    see  also  fissures. 
layer,  subcortical,  medullary,  168. 
lesions,  symptoms,  405. 
mantle  (pallium),  159-168. 
morphology,  183-207. 
relation  to  lower  centers,  145. 
cerebellum,  145,  315,  326. 
interbrain,  135,  143-145. 
midbrain,  145. 
schema,  145. 
section,  *19,  53,  *84. 

frontal,  *2,  *22,  *104,  *120,  248,  *258. 
structure,  184-191. 
sulci,  see  sulci. 
surface,  191-207. 
ventricle,  see  ventricle. 
Chorda  tympani,  relation  to  glosso-pharyn- 

geus,  378. 

Chiasma,  optic,  *18,  *20,  *70,  119,  124,  126,  I 
*76,  128,  *80,  137,  139,  *87-*91, 
140-142,   *99,   *104,   *113,   *114, ! 
*120,  188,  '127,   197,  *135,  241, , 
*162,  *168,  268,  *174,  276,  *178,  \ 
*180,  *181,  282,  *183,  285,  '195 
410. 


Cilia  of  epithelium,  central  canal,  340. 
Cingulum,   *144,   220,  239,   *156,   *170    265 

•178. 
!  Circulation,  disturbances,  lesion  of  medulla, 

405. 

Claustrum,  169,  '127,  190,  *160,  250,  '162, 
*169,  '171,  '172,  266,  *173,  *174, 
277. 

Clava,  373. 
Cleft,  branchial,  57,  58. 

visceral,  *26a. 

Cochlea,  40,  *  16,  91,  386,  *247. 
Collaterals,  21,  24.  55,  62,  68,  69,  93,  142,  143, 
213,  231,  233,  247,  287,  313,  320, 
326,  341,  342,  343,  351,  352,  355, 
357,  387,  394,  397,  406. 
Columns  (columnse)  of  cord  and  medulla, 
anterior,  82,  246,  305,  *216,  344,  '223,  351, 

356,  358,  *231,  367,  '233,  383. 
antero-lateral,  71,  *223,  351,  356,  *235,  379. 
Burdach's,   347-349,   *225,   350,   352,   *233, 
368;     see   also   funiculus   cune- 
atus. 

Clarke's,  see  vesicular,  of  Clarke, 
comma,  354. 
dorsal,  gray,  63,  64,  *28-*31,  66,  *40,  78,  79, 

*41. 

Goll's,  347,  348,  *225,  '226,  '350,  352,  '233, 
368;    see  also  funiculus  gracilis. 
lateral,  98,   108,  121,  246,  263,  *216,  341, 
*220,    344,    345,    *223,    349-350, 

354,  355,  358,  366-368,  373,  380, 
381. 

motor,  medulla,  85,  94.  95. 

posterior,  75,  78,  81,  98,  *43,  108,  272,  319, 
*215ft,  216,  341,  344,  346-348, 
*225,  *226,  351,  353-357,  360, 
367,  368,  *234,  ^70-373,  *238, 
374,  *239,  377,  379,  '241,  382- 
384,  397,  399,  408. 

Schultze's,  354. 

Tiirck's,  72. 

ventral,  gray,  63,  *28,  *29,  66-68,  *40,  79, 
*41,  *43,  84. 

vesicular,  of  Clarke-Stilling,  66,  328,  *216, 

341,  349,  355,  357,  408. 

Columns  fornicis,   172,  *125,  186,   187,  196, 
*144,  *172,  268,  *178,  279,  291. 
Commissura   ansulata,    172,   *125,    186,    187, 
196,  *144,  *172,  268,  '178,  279, 
291. 

anterior  cerebral,  3,  *18,  *76,  *84.  *86,  *95, 
*98*,  '100,  152,  153,  '101,  '114, 
171,  172,  '120,  *121,  '123,  *125, 
187,  '127,  190,  197,  216,  '144, 
'154,  '157,  241,  242,  '162,  '165, 
'167,  '168,  '172,  267,  '174,  269, 
»175-'179.  278,  "183,  *185,  '190. 
spinal,  *30,  *31,  70,  71,  337,  '216,  351, 

355,  356,  358. 
striatic,  *90. 

worm,  323. 

cerebral.  227,  241,  242. 
cord,  spinal,  discovery,  4. 
cornu  Ammonis,  171,  217. 


428 


GENERAL    INDEX. 


Commissura,    corpus    callosum,    see    corpus 

callosum. 
cray-fish,  26. 
epistriatic,  *101. 
Fritsch,  *85,  *91. 
grisea  thalami,  132. 
Gudden,  138,  260,  *169,  285,  *195,  303. 
habenularis,   126,   127,   *76,   129,   *79,   131, 

*86,   *93,   *95,   *99,   *114,   *125, 

188,  *144,  276. 

hemispheres,  159,  160,  172,  241-243,  247. 
inferior  (Gudden's),  285,  *195. 
mantle  (pallium),  168,  172.   . 
medulla,  dorsalis,  75. 

ventralis,  80. 

Meynert's,  *141,  260,  *169. 

mollis  (media),  132,  *125,  188,  250,  260, 
268,  *174,  *176. 

optic,  143;    see  chiasma. 

post-chiasmatic,  138. 

posterior  cerebral,  *18,  115,  119,  122,  123, 
*73,  125,  *76,  *85,  *86,  *89,  *95, 
*101,  *114,  *115,  *172,  125,  188, 

189,  295,  *191,  304,  305,  308,  312, 
313,  317,  397. 

spinal,   *29-*31.   66,   72,   337,   *216,   348, 

358,  372. 
Conarium,  *125,  276;    see  also  epiphysis  and 

glandula  pinealis. 
Conduction-paths,  356-358. 
Conductor,  sonorous,  388. 
Consciousness,  208,  209. 
Contractures,  muscular,  lesions  of  pyramidal 

tracts,  361. 
Control,  sensory,  44. 
Conus  frontalis"  pallii.  169. 

terminalis,  334,  *215&,  338,  354. 
Convolutions,  see  also  gyri. 

anatomy,  comparative,  210,  223,  224. 
brain,  base,  *135. 
Broca,  406. 
central,  205. 
literature,  223,  224. 

relation  to  intellectual  status,  205,  206. 
Convulsions,  cerebellar  tumors,  331. 
Co-ordination-centers,  100,  104,  105,  110,  309, 

357,  384. 

Coraco-brachialis,  spinal  center,  336. 
Cord,  spinal,  41,  47,  57,  62-74,  *37,  *39,  252, 
*182,   317,   "211,   332,   334,   338, 
363,  *236. 

association-bundles,  345,  353,  358. 
authorities,  359. 
cell-groups,  339,  340. 
cells,  peripheral  sympathetic,  333. 
centers,   for  extensors  of  arm   and   hand, 

340. 

flexors,  340. 
muscles,  336,  337,  340. 
reflexes,  336,  337. 
serratus  magnus,  336. 
skin,  sensation,  336,  337. 
columns,  see  columns, 
commissures,  see  commissura. 
degenerations,  346,  *228. 


Cord,  spinal,  effect  of  removal,  100. 
efficiency,  lower  vertebrates,  47. 
fibers,  see  fibers, 
field,  oval,  354. 
fissures,  see  fisssures. 
functions,  70,  75,  336,  337. 
horns,  see  cornua  and  horns, 
intumescentise      (enlargements),     47,     67, 

334. 

lesions,  334,  345,  346,  *224,  *228,  360. 
neuroglia,  343,  344. 
nucleus,  see  nucleus, 
radix  or  root,  see  radix  (root), 
reflexes,  70,  71. 
centers,  336,  337. 
paths,  355. 

relation  to  cerebrum,  74,  145. 
midbrain-roof,  118. 
sections,  *3,  *13,  337,  *216,  217,  344,  *223, 

*226,  *227,  354,  *230,  *258. 
size,  74. 

structure,  62-74,  344,  359. 
substance    (matter),  gray,  63,  338,  351. 

white,  63,  337,  338,  342. 
surface,  *215a,  *215ft. 
system,  motor,  66,  68. 
terminology,  70. 
"tract-cells,"  358. 

transition  to  medulla,  363-366,  379. 
zona,  anterior  radicular,  350. 
lateral  marginal,  350. 
marginalis,  355. 
spongiosa,  355. 
terminalis,  355. 
Cords,  vocal,  tracts,  246. 
Cornea  of  epiphysis.  reptiles,  127. 
Cornu  Ammonis,  *9,  29,  152,  170,  171,  *119, 
*120,  177,  *123,   186,  199.  *134, 
200,  212,   *141,  215,   *143,   217, 
218,    *144,    220,    226,    234,    235, 
*154,   236,   *156,   239,   242,   243, 
*158,  247,  249,  *161,  *165,  *175, 
-"•176,  274,  *177,  *179,  278,  283, 
*185,  *188,  292,  293,  *191. 
Cornua,  cord,  spinal,  *86,  *95,  *223,  *235. 
Corona  radiata,  3,   135,   173,   176,    178,   190, 
*156,     243-247,     *159,     248-252, 
*163,  254,   257,   259,   *168,  261, 
•169,  264,  265,  *176,  *183,  290, 
296,  407. 

Corpus  callosum,  3.  7,  *1,  53.  *24.  160.  172, 
*124-*127,  184-186,  190,  *132, 
196-198.  *133,  200.  *135,  203, 
211,  216,  *143,  218,  *144,  220, 
*156-*158,  240-242,  246,  *160, 
249,  *162,  254,  *165,  258,  *168- 
*172,  264-268,  *174-*176,  *178- 
*180,  283,  *185-*189,  290-294, 
*191. 

candicans,  *158,  274. 

dentatus    cerebelli,    299,    *193,    322,    *209, 
326,  328;    see  also  nucleus  den- 
tatus cerebelli. 
fimbriatum.  *123. 
fornicis,  186,  *144,  220. 


GENERAL   INDEX. 


429 


Corpus  geniculatum,  *70,  *7l,  *75,  134    *83 

*84,  136,  142,  *177,  288,  291. 
externum,  *70. 

laterale,  *81,  *82,  133,  "83,  *92,  143,  188, 
*165,   259-261,   *176,   *177,   282, : 
283.  285-290,  *183-*186,  297,  298, 
*191,  *192,  *195,  *198,  *247,  409. 
mediale,  133,  *165,  *182,  285,  *183,  *185,  ! 
289,  290,  *186,  *191,  *192,  298, 
*195,  *198,  408. 

habenulae,  126,  *79. 

interpedunculare,  *59,  *65,  *76,  131,  *83,  ' 
*114,  *144,  *201a;  see  also  , 
ganglion  interpedunculare. 

Luys,  *17.6,  *177,  276. 

mamillare,  132,  *93,  *120,  172,  *141,  *144,  ! 
218,  220,   221,   *169,  268,   *174, 
*176-*178.    274-277,    280,    *180, 
*190,  296,  *191,  305,  *199,  309, 
*201a,  312. 

opticum,  *25,  56,  *37,  *107,  *108-*112. 

pineale,  187,  188;  see  conarium,  epiphysis, 
and  glandula  pinealis. 

posticum  (midbrain),  *72. 

quadrigeminum,  3,  *19,  50,  *21,  113,  143, 
*125,  187,  189,  *144,  254,  257, 

275,  276,  283-290,  *183,  294,  295, 
*190,  *191,  297,  299,  *193,  304, 
305,   *197,   *199,   310-312,   *202, 
315,  316,   *205.   318,   *209,   324, 
330,  331,  370,  *236,  373,  384,  388, 
398,  *256,  401,  408,  409. 

anterius,  *65,  136,  *165,  *182,  284,  285, 
*183,   287,   288,   *185,   290,   294, 

295,  *191,  297,  298,  *192,  *194, 
195,  305,  *199,  308,  350,  387;  see 
brachium  anterius. 

posterius,  *65,  114,   124,  *182,  284,  285, 
*183,    *187,    300,    *194,    *201a,  ! 
*201&,  313,  *247,  387,  388,  409. 

restiforme.  *84,  137,  *182,  *183,  *204,  315, 
*210-*212,  326-329.  *234,  *236, 
*239,  379.  *241-*243,  381,  382, 
384,  385,  *244,  *245,  388,  *247, 
390,  391,  393,  397;  see  also 
peduncle,  inferior  cerebellar. 

striatum,  3,  47,  *20,  50,  51,  *22,  53,  54,  *25, 
56,  *37,  *44,  6d,   123,  *80,   132,  ; 
134,  *83,  *84,  136,  *86,  *87,  *89, 
*90,  *92,  *93,  *96,  144-160,  *96, 
*98-*100,    *102-*105,    *107-*112,  ', 
163,    165,   167,    169,   *118,   *119, | 
*121,  "122,  178,  183,  "126,  187, 
189-191,   -127,   *141,   M44,   220, 
*154,  *160,  *161,  261.  *169,  267, 
269,  270,  272,  274,  277,  278,  282, 

296,  *199. 
subthalamicum,  123,  *167,  *175,  272,  274, 

276,  *178,   *179,  278,  287.  288, 
299. 

trapezoides,  *53,  93.  96,  *141,  311,  318,  *206, 

*245. 
Cortex  cerebelli,  91.  105.  108.  318,  319,  321, 

*207.  *208.  322,  326,  329. 
vermis,  326,  327. 


Cortex  cerebri,  51,  72,  *99,  152,  *103,  *104 
161,  163,  165,  166,  168,  *124, 
*229. 

cells,  arrangement,  227. 
outer  layer,  231. 
polygonal,  228. 
pyramidal,  *9,  29,  168,  227,  228,  231, 

236. 

development,  206. 
dorso-inedian  area,  *103,  169,  *118,  *120 

174. 
fibers,  227,  233,  296. 

tangential,   168,   169,  *118,  227    *151 

231,  232,  *154,  236. 
fibrse  propriae,  237-239. 
forebrain,  structure,  227-237. 
fundament,  168,  205. 
histology,  227-237. 
injury,  effect  of,  224,  225. 
lateralis,  *118. 
layer,  fourth,  228. 

medullary,  deep,  227,  231,  236. 
molecular,  168. 
outer,  231. 

pyramidal,  168,  227,  231. 
second,  231. 
subcortical,  168. 
tangential,  168,  169,  *118. 
literature,  247. 
net-work,  interradial,  *151,  232,  233. 

supraradial,  *151,  232,  233,  239. 
neuroglia,  236. 
phylogeny,  174,  209. 
physiology,  173,  174,  205,  208-211,  224- 

226,  Z45. 
plate,  dorsal,  169. 

lateral,  169. 
radii    (rays,  medullary),  210,  229,  232, 

233,  236,  244. 
specialization,  173. 
structure,  167,  168,  *117,  227,  *150-*152, 

229-231,  233,  319. 
weight,  data,  206. 
cornu  Ammonis,  234,  236,  239,  247. 
fissura  calcarina,  region  of,  234. 
gyrus  centralis,  *153. 

hippocampi,  199,  220,  291. 
insulse,  266,  277. 

olfactory,  29,  131,  *100,  166,  169-172,  174, 
201,  213,  *142,  215,  217,  221,  236, 
282. 

Crista  acustica,  40,  409. 
Crus,  anterior,  capsula  interna,  *170,  *171. 
cerebri,  188,  242,  *164,  254,  255,  263,  280, 
•180,  282,  283,   *182,   287,  288, 
*185,  291,  294,  399-401;    see  also 
peduncle,  cerebral, 
commissura  anterior,  189. 
fornicis,  186,  220,  291. 
Crusta,  254,  263,  276,  *192,  302,  308,  311,  401, 

406,  407;    see  pes  pedunculi. 
Cubitus,  center,  cortical,  *148. 
Culmen  monticuli,  316,  *203,  *210. 
Cuneus,  *133,   198,  *135,  225,  232,  246,  288, 
292,  *189. 


430 


GEXERAL    IXDEX. 


Declivity  (declive),  cerebellum,  316,  *203. 
Decussation,  bundle  of  Meynert,  306. 
cerebellar,  dorsal,  110. 
median,  *61. 
ventral,  109. 
chiasma,    optic,    138-142,    282,    410;      see 

chiasma. 

commissura  anterior,  cerebellum,  *209. 
habenularis,  188. 
ventralis,  spinal  cord,  33,  69,  71. 
cord,  spinal,  motor  fibers,  66,  69,  70. 

sensory,  66,  356. 
cornua  Ammonis,  191. 
fasciculus  retroflexus,  131,  132,  306. 
fibers,  arciform,  81,  99,  368. 
auditory,  92,  *53,  96,  109,  387. 
glosso-pharyngeal,  378. 
olfactory,  146,  213. 
pneumogastric,  87,  378. 
trigeminal,  98,  393,  394,  396. 
trochlearis,  56,  *56,  *60,   108,   109,   121, 

313,  *201&. 

fibrae  acustico-spinales,  82. 
fila  olfactoria,  146. 
fillet   (lemniscus),  *233,  368-370,  382,  399, 

408. 

fornix  longus,  220. 
"fountain-like"  tegmentum,  308. 
hypothalamica,  *92,  276. 
layer  (stratum),  deep  medullary,  117,  *73. 

124,  *89,  301,  308. 
medulla,  sensory  fibers,  356. 
midbrain,  *67,  118,  120. 
peduncles,  cerebellar,  anterior  or  superior, 
*65,    122,    *84,    137,    299,    *193, 
*201«,  326,  399,  400,  *255,  *256. 
cerebral,  *187. 
post-chiasmatica,  *87. 
post-optica,  *80,  *86,  *95. 
psalterium,  218,  220. 

pyramids,  see  decussation  tract,  pyramidal. 
raph6,  medulla,  80,  81. 

tegmentum,  117,  118,  *201&,  308,  403. 
regio  subthalamica,  272,  *176,  274. 
supra- infundibularis,    132,    138,    *87,    *90, 

•91. 

taenia  habenulae,  276. 
tractus  cerebello-tegmentalis,  109,  311. 
cortico-spinalis,  83. 
habenulo-peduncularis,  131,  132,  306. 
nucleo-cerebellaris  nervi  trigemini,  109. 
pallii,  *90,  *93. 
pyramidal,  83,  *190,  330,  334,  344,  345. 

*231,  *232,  366-370,  377,  402. 
tegmento-cerebellaris,  *59,  107,  122,  *92. 
vago-tectalis,  86. 
transversa,  *72,  124,  133,  138,  *87-*90,  *93. 

*99. 

tubercles,  auditory,  *54. 
tuberis,  *91. 
valvulfe,  *60,  76.  *114. 
veli,  *56,  108,  121 ;    see  decussation,  nerve, 

trochlear. 

Decussation-zone,  cerebellum,  *210. 
Degeneration,  cerebellum,  322,  324. 


Degeneration,  cord,  spinal,  108,  *222,  346, 
347,  *224,  349,  351,  *228,  352, 
360. 

ganglion-cells,  6,  7. 
neuron,  23. 
parts  of  cerebrum,  155,  237,  257,  259    260 

306. 

pes  pedunculi,  298,  326. 
tract,  optic,  7,  287,  294. 

pyramidal,  246,  *221,  344,  352,  353,  366, 

367. 

Wallerian  law,  6,  7,  333. 

Degeneration-method,  6,  7,  9,  67,  68,  82,  91, 
107,  109,  141,  142,  155,  156,  272, 
287. 

Deglutition.  376,  402,  403. 
Deltoid,  spinal  center,  336. 
Dendrites,  20-24,  28,  *11,  *15,  *16,  62,  68,  73, 
94,  104,  124,  134,  143,  147,  150, 
168.  213,  227,  231,  234,  235,  236, 
308,  320,  358. 

Development,  brain,  47-61,  83,  84. 
cortex  cerebri,  209. 
mantle,  51,   146,   151,  *106,   177,  209,  221, 

222. 
nerves,  peripheral,  56. 

spinal,  sensory,  63,  64. 
Development-method,  9,  12,  91,  107,  155   287 

298. 

Diaphragm,  spinal  center,  336. 
Diencephalon,  *18,  *20,  *75,  *92,  *106. 
Digiti,  cortical  center,  *148. 
Disk,  choked,  cerebellar  tumors,  331. 
Diverticulum,  fourth  ventricle,  *53,  *54. 
Dorsum  linguae,  taste-fibers,  378. 
Dura  mater,  *215a. 
Dysarthria,  403,  405. 

Ear,  *16,  40,  59,  91,  92,  *149,  391. 

Ectoderm,  39. 

Embolus  cerebelli,  322,  *209. 

Emesis,  cerebellar  tumor,  330. 

Eminentia  teres,  376,  377. 

End-apparatus,  primary,  of  brain,  176. 

End-plates  of  nerves,  21,  23,  24,  90. 

Enlargements,  spinal,  see  intumescentise. 

Ependyma,  116,  388. 

Epiblast,  15,  49. 

Epidermis,  sensory  cells,  39. 

Epilepsy,  238,  239. 

Epiphysis,  *18,  *20,  *25,  *37,  115,  127,  *76, 
129,  130,  *79,  *107,  *109-*112, 
*114,  *125,  188,  *144,  276,  *186, 
295;  see  also  conarium  and 
glandula  pinealis. 

Epistriatum,  *86,  *95,  *97-*101,  149,  151,  152, 
*103,  156,  169,  *118,  *120,  215. 

Epithalamus,  *75,  126,  129,  130,  151. 

Epithelium,  central  canal  and  ventricles,  16, 
*5,  63,  78,  168,  210,  213,  *142, 
214,  236,  242,  260,  289,  319,  344, 
376. 

Equilibrium,  39,  44,  70,  91,  94,  102,  10.8,  110, 
309,  381,  409. 

Erectores  spinae,  spinal  center,  337. 


GENERAL   INDEX. 


431 


Evolution,  reflex-action,  32. 

medulla,  from  cord,  363-366. 
Experiment  of  Waller,  333. 
Extensors,  spinal  centers,  336,  337. 
Extremities,  cortical  centres,  *148,  *149,  251. 

motor  tract,  *163,  402. 

sensory  fibers,  348,  349. 
Eye,  140,  308,  409. 

parietal,     127;      see     epiphysis,     glandula 

pinealis,  and  conarium. 
Eyeball,  139. 

Face,  cortical  center,  *149. 
nerves,  tactile,  409. 
reflex,  sensory-motor,  397. 
Face-musculature,  lower  vertebrates,  95. 
Facialis,  see  nerve,  facial. 
Facies  caudalis,  cerebellar  plate,  *56. 

frontalis,  *56. 
Fascia  dentata,  200,  216. 
Fasciculus  antero-lateralis,  medulla,  '244. 
arcuatus,  239,  *156,  *170,  '171,  265,  266, 

267,  *173,  290. 
assoeiatus  nuclei  caudati,  *125,  *169,  *176, 

•177. 

cerebellar,  321,  *208,  322. 
cortico-pontile,  311. 
cortico-spinal,  366. 

fronto-occipital,  242,  *171,  267,  *173,  *178. 
longitudinalis  dorsalis,  376,  377. 

inferior,  *154,  239,  *156,  240,  *158,  *186- 

*189,  290,  292,  293,  294. 
posterior,  71,  *39,  *42-*44,  82,  93,  51-54, 
99.  *59,  65,   117,  *72,   122,  123, 
*73,  124,  *76,  *83,  136,  137,  *85, 
*87,  *114,  *115,  '144,  *175,  *177, 
*179,  278,  *191,  *192,  304,  305, 
*197-*199,  308,  *201ffl, *201&,  312, 
313,  *202,  350,  *243,  383,  *244, 
*245,  '247,  389,  *248,  *252,  *253, 
399,  400;    see  also  bundle, 
superior,  305. 
occipito-frontalis,  294. 
olfactory,  149,  150,  *98,  *99. 
retroflexus.  *80,  131,  132,  *141,  *144,  *177, 
•191,    306-308,    *199;     see    also 
tractus  habenulo-peduncularis. 
uncinatus,  239,  *156,  *171,  265,  *173. 
Vicq  d'Azyr,  132,  *144,  *158,  *169,  *176; 

see  also  bundle. 

Fasciola  cinerea,  *186,  *187,  292. 
Feet,  ambulacra!,  reflex-movements,  35. 
Fibers,  association,  98,  110,  173,  235,  237,  238, 

246,  247,  358,  359. 
Bergmann-Deiter,  329. 
cord,  spinal,  motor  fibers,  37,  68,  *33,  73, 

337,  338.  351-362. 

sensory,  57,  63,  68.  73,  81,  327,  332-334. 
341,  346-349,  351-362,  368,  370, 
372. 

inhibitory,  cardiac,  365. 
Mauthner's,  70,  94. 

nerves,  cranial,  see  also  nerves,  cranial, 
auditory,    109,   251,   311,   388,   398,   399, 
409. 


Fibers,   nerves,   facial,   251,    *163,   267    376 

406. 

glosso-pharyngeal.  409. 
hypoglossal,  87,  251,  '163,  267,  376,  377, 

*240. 

oculo-motor,  '191,  313. 
olfactory,  146,  148,   152,  153,  171,  *142, 

213,  217,  218,  221,  236,  251 
optic,  *65,  *66,  115,  143. 
pneumogastric,  86,  87,  375,  376,  383,  409. 
spinal  accessory,  365,  374. 
trigeminal,  399,  409. 
trochlear,  313. 

transverse,  pons,  280,  366,  373,  385. 
Fiber-system,  capsula  interna,  269,  276. 
cerebellum,  315,  323. 
cord,  347,  350-362. 
literature,  247. 
corpus    striatum,    154-156,    '105,    255-257, 

'166,  *169,  278. 
crusta,  311. 
fimbria,  171. 
fillet,  290. 
mantle,  211,  260. 
medulla,  98. 
midbrain,  116,  118,  276. 
nerve,  optic,  143,  287. 
pons,  311,  312. 
retina,  261. 
tegmentum,  *168. 
Fibrse  acustico-sacrales,  *29,  70. 
acustico-spinales,  82. 
arcuate  (arciformes),  368,  *234,  379,  '241, 

380,  381,  383. 
externse,   *52,  99,   108,  367,   '233,   '235, 

*237,  379,  *243. 
internae,  81,  *42,  *43,  85,  99,  368,  '234, 

'235,  *243,  382-384. 
intracorticales,  233. 
associate  breves,  *43. 
ponti;  280. 

propriae,  cortex,  237-239. 
semicirculares,  cerebellum,  *209,  '210. 
Fibrillae  of  cell  and  neuraxon,  21,  23,  25,  37, 

63. 

Field,  association,  medulla,  366. 
auditory,  92,  97,  *54. 

olfactory,  190,  215,  217,  220,  221,  '169,  262, 
276,  282;  see  also  area,  olfac- 
tory. 

oval,  cord,  lumbar,  354. 
Fila   olfactoria,   22,    146-148,   *94,   *96,   »98, 

*100,  152,  212,  *142. 

Fillet,  71,  72,  81-83,  86,  93,  98,  99,  '65,  "67, 
*71,  124,  *84,  220,  244,  246,  260, 
*168,  263,  '175,  *177,  '179,  290, 
*191,  *192,  302,  308,  309,  312, 
313,  *202,  314,  *205,  '233,  368- 
371,  *238,  '239,  381-384,  *244, 
387,  *253,  399,  400,  406,  408, 
409;  see  also  lemniscus  and 
laqueus. 

inferior,  or  lateral,  *191,  299-301,  '198,  308, 
*201ff,  '201&,  313,  315,  388,  398, 
'253,  408. 


432 


GENERAL    IXDEX. 


Fillet,  superior,  or  median,  262.  263,  272,  *177, 
278,  *191,  299,  *198,  308,  *201a, 
*201ft,  313,  397,  398,  *253,  399, 
403,  408. 

Filum  terminale,  334,  *2156. 
Fimbria,  171,  *120,  186,  *133.  *134,  199,  200, 
*143,  218,  *154,  *169,  *176,  *177, 
291,  *191. 

Fingers,  cortical  center,  *148. 

Fissures,  192;    see  also  sulcus. 

arcuata,  202,  203,  221-223. 

septi,  *76,  *114,  165,  166,  171,  *120. 
calcarina,  *133,  198,  *135,  203,  234,  *189, 

293. 
centralis,    193,   204,   *138,   *145,   222,   223, 

*186. 

cerebellar,  320,  323. 
chorioidea,  201,  202. 
collateralis,  201,  *135,  *186. 
cord,  spinal,  *2156,  337,  *216,  344,  346. 
coronalis,  221. 
cruciate,  *147,  223. 
development,  203. 
ectosylvia,  223. 
fronto-occipitalis,  240,  242. 
hippocampi,  199-201,  *154. 
interparietalis,  *138,  205,  222,  *186-189. 
limbica,  166,  171,  200,  *141,  213,  216,  *143; 
see     also     sulcus     calloso-mar- 
ginalis. 

longitudinal,  great,  161,  186,  190. 
mantle,  221. 
marginal,  200. 

occipito-frontalis,  *165,  *185. 
ontogeny,  203. 
parieto-occipitalis,    *129,    *133,    198,    *135, 

*188,  203. 

perpendicularis  externa,  198,  203,  *138. 
primary  or  primitive,  *22,  203. 
retrocentralis,  195. 
sagittal,  113,  221,  223. 
simian,  198. 

splenialis,  see  sulcus  calloso-marginalis. 
suprasylvia,  223. 

Sylvii,  *23,  53,  183,  191,  192,  *129-*131,  194, 
*135,    *138,   221-223,    *145-*147, 
204,  *172,  *186-*188. 
insulse,  *171. 

temporalis  superior,  *188,  *189. 
transitory,  *136,  203. 
Fleece  of  Stilling,  381. 
Flexors,  spinal  centers,  336,  337. 
Flocculus    cerebelli,    317,    *204,    *211,    *234, 

*244. 

Floor,  interbrain,  187. 
metencephalon,  310. 
of  aquaeductus  Sylvii,  *196,  303,  304. 
ventricle,  fourth,  373. 

third,  260,  280. 

Fluid,  eerebro-spinal,  319,  372. 
Folium  cacumenis,  *203,  316,  317,  319. 

vermis,  316. 
Foramen  of  Majendie,  319,  372. 

Munro,  126,  187. 
Forceps,  corpus  callosum,  *158,  *189. 


Forceps,  major,  241,  293,  294. 

minor,  241. 

Forearm,  cortical  center,  *148. 
Forebrain,  47,  49,  50,  *24,  114,  134,  145-179, 
*96,  *97,  183,  *126,  *132,  201, 
208,  209,  227-237,  242,  243,  254- 
256,  258,  *176,  276,  283,  *183, 
*185. 

cortex,  structure,  227-237. 

sections,  *102,   166,  167,  *124,  *157,  *162, 

*165,  *185. 
Formatio  bulbaris,  147,  152,  *100,  *113. 

cerebelli,  75. 

reticularis,  76,  83,  384;  see  also  substantia. 
Fornix.  52,  53,  *24,  *81,  *100,  *101,  171,  172, 
*120,  *125-*127,  186,  187,  190, 
*132,  196,  197,  *133,  199-201, 
215,  *143,  217,  218,  *144,  220, 
221,  *154,  242-244,  *158,  249, 
250,  *162,  *165,  *168,  *169,  *172, 
267,  268,  *174-*176,  274-277, 
*178,  *179,  279,  280,  *185,  291, 
*190. 

longus,  218,  220,  242,  *191. 
Fossa  rhomboidalis,  73,  313,  *205,  319,  388, 
399;     see   sinus,   and   ventricle, 
fourth. 

Sylvii,  *23,  53,  191,  204,  243. 
Fovea  collateralis,  164,  165. 

limbica,  162,  *113. 
Function,  cerebellum,  102,  104,  105,  110. 

cord,  spinal,  70,  336,  337,  347,  348,  358. 

cornu  Ammonis,  226. 

corpus  quadrigeminum  anterius,  285,  309. 
posterius,  285,  309. 

corpus  striatum,  158. 

cortex,  cerebral,  173,  206,  208-211,  224-226, 
240,  245. 

cuneus,  225. 

epiphysis,  127. 

fasciculus  longitudinalis  inferior,  240. 
posterior,  304,  305. 

fillet,  299,  300. 

foramen  of  Majendie,  319,  372. 

formatio  reticularis,  384. 

fornix,  218. 

funiculus  solitarius,  376,  378. 

ganglia,  spinal,  334. 

ganglion-cells,  31. 

head-canals,  95,  96. 

hypophysis,  281. 

insula  (left),  225. 

interbrain,  134,  135. 

labyrinth,  91. 

line,  lateral,  93. 

medulla,  94,  100. 

plexus,  peripheral  nerves,  334. 

stratum  (layer)  medullare  profundum,  116. 

substantia  reticularis  frontis,  315. 

thalamus  opticus,  261,  262. 
Fundament,  branchial,  59. 

cord,  spinal,  88. 

cortex,  cerebral,  168,  205. 

epibranchial,  57. 

Fissura  centralis,  204. 


GENERAL    IXDEX. 


433 


Fundament,  Froriep's,  57,  58,  *26a. 
head,  59. 
hypophysis,  *21. 
Kupfl'er's,  57,  58,  *26a. 
lateral,  57. 

peduncle,  cerebellar,  superior,  314. 
pes  pedunculi  or  crusta.  276. 
sense-organs,  primitive,  57. 
Funiculus  cuneatus,  *182,  *215&,  *216,  *223, 

347,  349,  *232,  *235,  *236,  *239; 

see  also  column  of  Burdach. 
dorsalis,    cord,    spinal,    *29,    *31,    65,    *43, 

*235. 
gracilis,  *182,  *215?>,  *216,  347,  348,  *223, 

*231,  *235,  *236,  *239;    see  also 

column  of  Goll. 

lateralis,  cord,  spinal,  *29,  *30,  *31,  *2156. 
posterior,  medulla,  79,  *41,  382. 
solitarius,  375,  376,  378,  384,  392. 
teres,  376. 
ventralis,  cord,  spinal,  29. 


Ganglion,  ganglia 
brain,  15,  47-61. 


,  26,  33,  35,  47. 


cerebellum,  326. 
commissura  posterior,  295. 
corpus  mamillare,  276,  277. 

quadrigeminum  posterior,  124,  300,  301, 

408. 

striatum,  156,  250. 
cray-fish,  26,  *8. 
earth-worm,  *12. 
ectomamillare,  138,  *87,  *113. 
epibranchial,  *26b,  *26c,  61. 
epistriaticum,  149. 
epithalamicum,  129. 
forebrain,  basal,  47,  134,  155. 
frontal,  99,  145. 

Gasserian,  61,  79,  85,  95,  364,  394,  409. 
geniculi  (geniculatum),  58,  392. 
habenuhe,  *70,  *75,  127,  *76,  129-132,  *79, 

*82,    *83,    143,    146,    151,    *100, 

*114,  *115,  172,  *125,  188,  *144, 

220,   221,   259,   260,   *169,   *176. 

*177,  276,  296,  *191,  306. 
hypothalamus,  132. 
interbrain,    *91,    155,    *166,    256,    258-263, 

*169,  295. 
interpedunculare,  *S3,  *141,  *144,  220,  306, 

307. 

intestinal,  26. 

isthmi,  *65,  *71,  *72,  124,  *84,  138. 
jugulare,  58,  85. 

maxillo-mandibulare,  *266,  *26c,  61. 
metathalamus,  154. 
mesencephali    laterale,    *67,    68,    117, 

*72,  *195. 
mediale,  *195,  302. 
profundum,  *85. 
midbrain,  47,  245.  *166,  257. 
nerves,  cranial,  37,  57,  59,  *26&,  *26c. 
auditory,  58. 
facial,  *26b,  *26f.  61. 
glosso-pharyngeal.  *26b,  *26c,  61. 
olfactory,  58. 


71, 


Ganglion,   nerves,   pneumogastric,    58,    *266, 

*26c,  61. 

ophthalmicum,  *266,  *26c,  61. 
optic,  301. 
peripheral,  26. 
petrosum,  58. 

pontile,  245,  280,  311,  326,  400,  401. 
regio  subthalamica,  257,  271,  272,  276,  277, 

*191. 

septum  pellucidum,  165. 
spinal,  15,  26.  *13.  37,  39-41,  *15,  57,  59,  62, 
*27,  332-334,  340.  341,  347,  407. 
spirale  cochleae,  *16,  386,  409. 
supra-03sophageal,  arthropods,   102. 
sympathetic,  35. 
tegmenti,  *73,  123,  400. 
thalamus,  119,  130,  132,  135,  *85,  *91,  154, 
156,  188,  244,  257,  259,  »169,  269, 
278,  289,  294,  296;    see  also  nu- 
cleus. 

Ganglion-cells,  4-7,  15-26,  *4,  *6,  *7,  29-31,  36, 

37,  39,  40,  *16,  55-57,  59,  61,  *27, 

63,  66,  67,  *32,  70,  73,  84,  103, 

104,  139,  168,  351,  391,  405,  407. 

Genu,  capsule,  internal,  251. 

corpus  callosum,  197,  264,  265,  283. 
nerve,  facial,  *248. 
sulcus  centralis,  193. 
Germ-cells,  medullary  plate,  15. 
Germ-layer,  epiblast,  49. 

Glandula  pinealis,  *25,  128,  *110,  *125.  »165, 
276,  *182,  *185,  *190,  *236;    see 
also  conarium  and  epiphysis. 
Glia,  17;    see  also  neuroglia. 
Globus  pallidus,  *104,  157,  *121,  190,  256,  257, 

*169.  *172,  267,  *173,  *176. 
Glomerulus  olfactorius,  *94,   147,  213,  *142, 

*144. 
Glosso-pharyngeus,  see  nerve,  glosso-pharyn- 

geal. 

Granules,  ganglion-cells,  25,  214. 
Groove,  median,  mantle,  159. 
medulla,  anterior  radicular,  373. 

primitive,  15,  49. 
neural,  15,  49. 
Ground-bundle,  cord,  spinal.  *223,  *225,  *226, 

350,  366,  368,  370. 
Gut,  preoral.  128,  129. 

Gyrus,  178,  179,  192,  194,  *135,  205-207,  221, 
225,  233,  237,  238;    see  also  con- 
volution, 
angularis,  *130,  *131,  195,  292,  293,  406. 

callosus.  200. 

centralis,  *129,  225,  226,  246.  253,  405.  406. 
anterior,  *129-*131,  193,  *145,  *147,  *153, 
237,  244,  251,  267,   *173,   *186, 
406. 
posterior,  *129,  193,  194,  *130,  *131,  *145, 

237. 

cinguli,  *133,  202,  *170,  »171,  *186-*188; 
see  also  gyrus  fornicatus  and 
cingulum. 

dentatus,  *133,  *134,  200,  203,  216,  »143, 
234,  *154. 


434 


GENERAL    INDEX. 


Gyms,  fornicatus,  *133,   198-200,  202,  *143, 
216,  220,  *170;    see  also  gyrus 
cinguli  and  cingulum. 
frontalis,  194,  201,  205,  223,  *151,  246,  253, 

*170,  266. 
inferior,  *130,  194,  *131,  *135,  *138,  225, 

245,  253,*172,  406. 
medialis,  *130,  *131,  *138. 

superior,    *130,    *131,    *133,    198,    *138, 

•180. 

fusiformis,  *133,  201,  *135,  *186-*189. 
hippocampi,   *133-*135,   199-203,   213,   215, 

216,  218,  220,  234,  235,  *154,  236, 

246,  *18tO,  282,  283,  292,  293. 
insulae,  223. 

brevis,  *129,  193. 
longus,  *129,  193. 
limbictis,  *123,  218. 
lingualis,  *133,  199,  *135,  *186-*189. 
marginalis,  195,  200,  202,  216,  218,  220,  223, 

226,  239,  274,  293. 

occipitalis,  *130,  *131,  *154,  288,  292. 
orbitalis,  *170,  *171,  267. 
parietalis,  superior  and  inferior,  *130,  *131, 

195,  *138,  253,  259. 
rectus,  *133,  201,  *135,  *171. 
subcallosus,  *133,  201,  *135,  217,  283. 
supramarginalis,  *130,  *131. 
temporalis,  superior,  middle,  and  inferior, 

*130,  194,  *131,  *133,  201,  *135, 

*138,  225,  246,  *188,  292,  409. 
uncinatus,  198,  200;    see  also  uncus. 

Habenula,  *44. 

Hair,  nerve-endings,  *17. 

Hair-cells,  organ  of  Corti,  40,  *16. 

Hand-muscles,  spinal  centres,  336. 

Hardening  methods,  3,  4,  264. 

Headache,  331. 

Head-canals,  sensory,  95,  96. 

Hearing,  cortical  center  and  tract,  *148,  253. 

Heart,  ganglion-cells,  37. 

Heat-loss,  43. 

Hemianesthesia,  330,  403. 

Hemianopsia,  245,  269,  293. 

Hemichorea,  270. 

Hemiopia,  253. 

Hemiplegia,  253,  254,  270,  330,  403. 

Hemisphere  (hemisphoerium). 

cerebellum,    102,   311,    315-318,   324,   *211. 

326,  *252,  381. 

cerebrum,  49-53,  *20,  *24,  *75,  146.  159-165, 
*113,  *118,  178,  *124-*127,  183- 
207,  *129,  *132,  *133,  215,  216, 
237-243,  *156,  *158,  *160,  *171, 
*180. 

Hemorrhage,  cerebellar,  329. 
cerebral,  54. 

Herpes  zoster,  334. 

Hilum,  gyrus  fornicatus,  198. 
oliva  inferior,  380,  381. 

Hindbrain,  49,  *141,  *144,  *182,  310,  *236. 

Histology,  cord,  authorities,  359. 
cortex  cerebri,  227-237. 

cornu  Ammonis,  authorities,  247. 


Histology,  fibers,  optic,  287,  288. 

History  of  investigation  of  nervous  system, 
3-14. 

Hoarseness,  405. 

Horn  of  Ammon,  *9,  29,  170;    see  also  cornu 

Ammonis. 

cord,  spinal,  anterior,  *6,  23,  25,  63,  66,  68, 
79,  84.  337,  338,  *216,  *218, 
*219,  343,  351,  355,  357-360, 
*229-*231,  365,  366,  *233,  373, 
374,  *239,  383;  see  also  columna 
ventralis. 

lateral,  85,  338.  364,  374,  *239. 
posterior,  63,  64,  78,  79,  85,  337,  338,  *216, 
340,  341,  *219,  343,  354,  355, 
357,  362,  *230,  363-366,  *236, 
368,  *238,  374,  375,  *239,  382, 
383,  407,  410;  see  also  columna 
dorsalis. 

ventricle,  lateral,  53,  156,  240. 
anterior,  162,  187,  265,  266. 
inferior    (middle),   *125,    186,    187,    199, 
*134,  200,   *154,   241,   249,   278, 
291-293. 

posterior,  162,   187,   198,  240,  241,  *188, 
292,  293,  *188. 

Hydrocephalus,  206,  207. 

Hypoglossus,  see  nerve,  hypoglossal. 

Hypophysis,  *18,  *21,  *25,  56,  *74,  *76,  128, 
*77,  *78,  129,  *93,  *108,  *110, 
*112-*114,  *127,  *162,  280-282, 
•181,  *183,  *190;  see  also  in- 
fundibulum. 

Hypothalamus,  *44,  *74,  126,  *75,  128,  132, 
134,  137-139,  *86,  *87,  *90,  *92, 
*95,  156,  271-279. 

Hysteria,  43. 

Idiocy,  206. 

Ileo-psoas,  spinal  center,  337. 

Impression,  sensory,  31,  39,  173. 

Impulses,  transmission.  23,  31,  33,  356. 

Individuality  of  cells,  231,  320. 

Infraspinatus,  spinal  center,  336. 

Infundibulum,  *25,  *37,  *77,  128,  129,  132, 
*85,  *109,  *110,  *112,  187,  188, 
*127,  190,  197,  *162,  268,  *174, 
280,  281,  *180,  •181,  282,  *190; 
see  also  hypophysis. 

Inhibition,  35,  71. 

Inner vation,  motor,  24,  *17,  67,  70,  84,  304, 

334. 

peripheral,  42. 
sensory,  41,  43,  336,  337. 

Insula  Reilii  (island  of  Reil),  4,  191,  192, 
*125,  *129,  193,  *130,  •131,  •138, 
204,  223,  225,  *156,  239,  246, 
•160,  249,  250,  *169,  *171-*175, 
266,  277,  •179,  406. 

Intellect,  relation  to  gyri,  205-207,  233. 

Interbrain,  3,  47,  50,  *24,  71,  80,  98,  99,  101, 
107,  114,  *70,  119,  120,  122,  123, 
125-144,  *74-*77,  *79-*87,  *89- 
*93,  145,  *95,  *98-*100,  *102, 
155-157,  *104,  *106,  167,  169, 


GENERAL    INDEX. 


435 


Interbrain  (continued'). 

*119,  172,  *122,  178,  '125,  186- 
188,  '126,  '132,  196,  197,  218, 
*144,  220,  221,  242,  250,  254, 
'165,  *166,  256,  257,  '169,  258- 
263,  271,  *175-*177,  274,  276, 
278.  '182,  *185,  295,  '191,  304-5. 

Intestines,  26,  37. 

Intumescentia    (enlargement),    spinal    cord, 
*32,  67,  *2156,  335. 

Isthmus,  *20. 

Karyokinesis,  brain-cells,  55. 
Kidneys,  nerve-endings,  4. 
Knee,  see  genu. 

Labyrinth,  44,  91,  102,  390. 
Lamina  (layer),  see  also  stratum, 
cerebellum,  318. 

granular,   *47,   104,   *60,   320,   321;     see 

also  zona  granularis. 
medullary,  320,  321. 

nucleus  dentatus,  323. 
molecular,  *47,  105,  *60,  108,  110,  321; 

see  also  zona  molecularis. 
plate,  103,  *56,  104,  110. 
cord,  spinal,  marginal,  *223. 
peripheral  gelatinous,  344. 
cortex  cerebri,  fourth,  228. 
medullary,  231,  234,  236,  238. 

deep,  168,  227,  231. 
molecular,  168,  236. 
outer,  231. 

pyramidal,  168,  227,  231. 
second,  231. 

tangential,  168,  169,  '118,  233. 
cribrosa,  *142. 

fillet,  lemniscus,  299,  309.  378. 
glomerular,  olfactory  bulb,  213. 
interolivary,    medulla,    *233,    *234,    *239, 

'243. 
medullaris  circumvoluta,  cornu  Ammonis, 

234,  235. 
involuta,  '154. 
mesencephalon,    midbrain,    commissuralis, 

118,  *76,  '114. 

medullary,  deep,  116,  117,  *68,  118,  123, 
*73,  124,  *80,  *89,  '144,  301, 
'195,  308. 

nuclei  tegmenti,  272. 
roof-plate,  115. 
ventral,  113. 
optica,  116,  *69,  *73. 
retina,  granular,  287. 
supraneuroporica,  127. 

terminalis,  *18,  49,  *20,  o3,  126-128,  145, 
153,  159-162.  165,  Ibd,  187,  196, 
197,  '133,  '135,  283. 

thalamus,   latticed,    '165,   259,   260,    '168, 
268.  *174,  *176,  277,  289,  '185. 
medullaris,  296,  308. 

externa,    262,    '175,    '176,      .78,    277, 

278,  '179. 

interna,  262,  269,  *174,  *176-'178,  277, 
'191. 


Laqueus,  '165.  '185,  '194,  '195,  '199,  '235, 
'244,    '245,    '247,    '248,    '252; 
see  also  fillet  and  lemniscus. 
Larynx,  cortical  center,  '148. 
Latissimus  dorsi,  spinal  center,  336. 
Law  of  Waller,  6,  7,  333. 
Lemniscus,  71,  81,  '192.  299,  300,  '194,  309, 
368,  378,  379,  382-384,  399,  '254- 
'256,  403,  407-409 ;  see  also  fillet, 
inferior,   or  lateral,   '191,  299,   300,   '194, 

313,  387,  388,  397,  409. 
superior,  or  median,   296,   '191,  300,  313, 

383,  398,  408. 
Lens  of  epiphysis,  127. 
Lesion,  base  of  brain,  283,  405. 
capsula  interna,  253,  294,  407. 
centrum  ovale,  403. 

semiovale,  252,  253. 
cerebellum,  322,  329.  330,  357. 
brachium  pontis,  329. 
hemisphere,  326.  381. 
peduncles,  299,  329. 
vermis,  326,  330. 
cerebrum,  cortex,  225,  253,  293,  294,  298, 

*222,  405,  410. 
crura,  283. 

pes  pedunculi,  309,  403. 
cochlea,  388.    . 
cord,  spinal,  334,  345.  346,  '222,  348,  '228, 

352,  356,  357,  360-362. 
corpus  callosum,  254. 
quadrigeminum,  309,  331. 
striatum,  257,  270. 
fillet,  lateral,  388. 
ganglion  habenulse,  306. 

spinal,  334. 
medulla,  402-405. 
neuron,  motor,  407. 
nucleus  of  Deiter,  328. 
glosso-pharyngeal.  403. 
hypoglossal,  403.  405. 
motor,  medulla,  407. 
oculo-motor,  309. 
trigeminal,  396,  403. 
pons,  402-405. 
paralysis  progressiva,  322. 
regio  subthalamica,  309. 
i      speech-pathway,  406. 

thalamus.  269.  270. 
Levator  palpebree,  innervation,  304. 
Ligamentum  dentatum,  *215o. 

tectum,  '124. 

Light-impressions,  transmission,  116. 
Limb,  capsula  interna,  251. 
anterior,  256,  265. 
posterior,  250-253,  294. 
corpus  callosum,  266. 
fissure  of  Sylvius,  192. 
Line  of  Baillarger,  232. 
Bechterew.  233. 
Gennari,  '151,  232-234. 
lateral,  57,  88,  89,  93,  94. 
Vicq  d'Azyr,  232. 

Lingula  cerebelli,  '202.  '203,  316,  318,  319, 
'209,  323,  '253,  399. 


436 


GENERAL    INDEX. 


Lingua,  cortical  center,  *149. 
Liver,  nerve-endings,  40,  42. 
Lobe,  lobus. 

cerebellar,  316,  317,  323. 
centralis,  316,  *204,  319. 
cuneiformis,  *204,  318. 
graeilis,  *204,  318. 
monticulus,  318. 
quadrangularis,  *203,  bi/,  *204. 
posterior  inferior,  *204,  318. 

superior,  *203,  317. 
semilunaris  inferior,  *203,  *204,  318. 

superior,  *203,  317. 
cornu  Ammonis,  152,  216. 
electricus,  *48,  89,  *58,  *108. 
frontal,  *23,  53,   153,   163,   178,  *125,   187, 
193,  194,  201,  205.  206,  210,  221- 
223,   *147,   227,  233,   *156,.  239- 

241,  245,    246,    *160,    249,    250, 
259,  *171,  265,  *180,  298,  *199, 
309,  311,  315,  407. 

hippocampi,  215,  220,  234;    see  also  gyrus. 

inferioris  mesencephali,  *68,  *85,  *86,  *91. 

infundibulum  or  hypophysis,  *127,  *162, 
280,  281. 

limbicus,  216,  *143. 

lingualis,  288. 

nervi  acustici  cerebellaris;  *58,  105. 
facialis,  97. 
trigemini,  *44,  *52,  *53,  97,  98,  105,  *58, 

*107,  *108. 
vagi,  18,  85,  *52,  *107. 

occipital,  *23,  53,  *84,  *106,  163,  *113,  175, 
177,  *123,  *125,  187,  195,  196, 
198,  201,  *135,  206,  225,  232, 
233,  237,  *156,  239-241,  243- 
245,  249,  *160,  251,  252,  260, 
*180,  285,  *183,  288,  290-294, 
408. 

olfactory,  22,  *20,  50,  51,  *44,  *74,  *80,  131, 
*86,  *92,  146.  147,  *95,  *96,  148- 
150,  *100,  152,  *101,  161,  162, 
*135,  209,  *140,  211,  212,  *141, 
215-218,  *143-*145,  *147,  239, 

242,  *161,  *172,  267,  *173,  274, 
*180,  282,  320. 

optic,  47,  113,  351. 

parietal,  53,   *23,   193,   194,  205,  221,  227, 

*15G,  239,   243,  260,   *168,   292, 

*199,  309,  311,  315,  326,  401,  408. 
pyriformis,  152,  *140,  213,  215,  218. 
supracallosus,  216;    see  also  gyrus  forni- 

catus. 
temporal,  *23,  53,  183,  *125,  187,  190,  192- 

194,  196-198,  133.  200,  201,  205, 

206,  221,  *156,  239-243,  245,  246. 

*160,  249,  251,  252.  *168,  *172. 

267,  *173,  269,  *175,  *178-*180. 

278,  279,  282,  285,  290,  292,  293, 

298,   *199,   309,  311,   315,   *247, 

401,  408. 

temporo-occipital,  407. 
Lobule,  lobulus,  paracentralis,  *133,  198,  225, 

246,  *187,  *188,  405. 


Lobule,    parietalis    inferior,     *130,     194-196, 

*131,  *186-*189,  410. 
superior,  *130,  194,  *131,  198,  237,  245, 

*187,  *188. 
Localization   of   lesions,   334,   336,   337,   402- 

405. 

Locus  coeruleus,  394,  *252,  399. 
Loop,   lenticular.    157,   267;     see   also   ansa 

lenticularis. 

Lungs,  nerve-endings.  41. 
Lyra  Davidis,  186;    see  psalterium. 

Macula,  of  ear,  *16,  409. 

Malformations,  of  central  nervous  system,  7. 

Mantle,  pallium,  50,  *25,  *37,  *76,  145,  146. 

151-153,  *99,  *101,  155,  156,  158', 

159-179,    *106,    *107,    *110-*112, 

*114,  *116,  *117,  *122,  203,  208- 

211,  221,  222,  226,  246,  256,  260, 

*169. 

Marrow,  deep  medullary,  71,  308;    see  also 

layer  and  stratum. 
Mastication,  393,  402,  403. 
Matter,  30,  57,  62,  *194,  *199;    see  also  sub- 
stance. 

gray,  aqueduct  of  Sylvius,  305,  308. 
cerebellum.  322,  323. 
cord,  spinal,  340-343,  349,  350,  352,  353, 

357,  358. 

corpus  quadrigeminum,  308. 
interbrain,  *91,  141. 
medulla,  367,  368,  371,  372. 
ventricle,  third,  260,  263. 
white,  cord,  spinal,  350,  363. 
Maturity  of  brain,  55. 
Mechanism,  congenital,  33. 
inhibitory,  35. 
motor,  35. 

olfactory,  151,  152;  see  also  apparatus, 
optic,  174,  175. 
sensory,  39. 

Medulla,  cornu  Ammonis,  217. 
hemisphere,  237-247. 
insulse,  266. 

olfactory,  213,  215,  220,  *176,  267. 
Medulla  oblongata,  5,  18,  47,  *18,  *25,  75-100, 
*37-*54,  108,  109,  121,  134,  *87, 
*92,  143,  *109,  *110,  178,  243- 
245,  257,  263,  274,  *180,  *182, 
*190,  311,  313-315,  319,  *211, 
328,  330,  341,  344,  345.  348,  350, 
356,  363-385,  *231-*244,  *246, 
391,  399,  401-405,  *258,  407- 
409. 
spinalis,  *18,  *39,  *44,  *211,  344;  see  also 

cord,  spinal. 
Medullation  of  nerve-fibers. 

cerebral,  233,  237.  238,  245,  246.  257,  *167. 

spinal,  345-347,  349,  350,  368,  370,  379,  380. 

tracts,  various,  295,  *199,  301,  305,  307-309, 

328,    345,    346,    350,    352,    353, 

368,    *234,    370,    378,    379,    383, 

399. 

Membrane,  mucous,  40.  41.  4.3.  213.  *142,  281. 
Memory,  cortical  center,  173,  175,  227. 


GENERAL    IXDKX. 


437 


Mesencephalon.  *25.  56.  71,  80,  81,  98,  99, 
*64.  *67,  *68,  114,  117,  118,  *69, 
•71,  *72,  *74,  *76,  *79,  *83,  '85, 
*88,  *89,  *92,  *95,  *97,  *106, 
*110,  *113-*115,  *121,  *123,  289, 
302,  *195,  310,  318,  *236,  *251, 
398,  399,  402;  see  also  mid- 
brain. 

Mesostriatum,  *  103,  156,  *  118. 

Metamere,  33.  34,  48. 

Metathalamus.  136,  137,  154,  271-279. 

Metencephalon,*18,*20,  50,  310,  317,  318,  399. 

Midbrain,  33.  47,  49,  51,  56,  71,  72,  *37,  80, 
81.  93,  98.  99,  101,  105,  107-111, 
112-124,  *65-*73,  125,  126,  *76, 
129,  131-134.  *83,  *85,  *86,  138, 
139,  *89,  *91,  143,  145,  *109, 
•111,  *114,  166,  174-176,  178, 
187-189,  197,  *144,  221,  242,  245, 
254,  '166,  257,  263,  276,  283, 
•182,  287,  289,  290,  295-309, 
*190-*199,  300,  315,  317,  368, 
383,  401,  402;  see  also  mesen- 
cephalon. 

Monoplegia,  254. 

Monospasm,  254. 

Monticulus  cerebelli,  *203,  316,  317,  319. 

Morphology,  comparative,  48,  164,  165,  177. 
general,  10,  11,  125,  161,  167,  183-207. 

Motor-oculi  nerve,  see  nerve,  oculo-motorius. 

Movement,  congenital  mechanism,  33. 
co-ordination,  *12,  *33-*35,  43. 
regulation,  357. 

Muscles,  contractures,  pyramid  lesions,  361. 
innervation.  37,  67,  68,  70.  90,  304,  305,  309, 

334,  336,  337,  340,  '229,  393. 
of  extension,  see  extensors, 
of  flexion,  see  flexors, 
spasticity,  361. 

Museulus  ciliaris,  304. 

Muscle-tonus,  91,  110,  357,  381. 

Myelencephalon,  *18,  *20. 

Myxcedema,  281. 

Neck,  cortical  center,  *149. 
Neighborhood-symptoms,  330,  331. 
Nerve,  the,  20-30   (nervus). 

cranial,  8,  37,  57,  59,  *26ft,  *26c,  61.  75-100, 
*63,  303,  304,  309,  326,  327,  '237, 
374-376,  383,  398,  399,  402,  *257, 
403-410. 

abducens,  *47,  *49,  94,  95,  *115,  *183, 
304,  330.  *237,  374,  *245,  386, 
'247,  389,  390,  '248,  392,  *249, 
*257. 

accessorius.  see  spinal  accessory. 

auditory  (acusticus),  *16,  58,  59,  70,  76, 
*39,  78,  '407} .  84,  85,  *46,  *48, 
91,  *49.  92,  *53,  93,  96,  *54,  105, 
*60,  108,  109,  *71,  245,  251,  285, 
311,  313,  *211,  326-328,  *237, 
374,  378,  384-391,  *244,  *245, 
*247,  *248,  392,  398,  399,  *257, 
409:  see  also  nerve,  cochlear 
and  vestibular. 


Nerve,    cranial,    cochlear    (cochlearis),    *16, 

*54,  386-388.  '247,  391,  409. 
facial  (facialis),  58,  59,  '266,  *26c,  61,  '»*, 

84,  *46,  *47,  *49,  '50,  95,  *54, 
97,   251,    *163,    267,    330,    '237, 
374,   376,  384,   '244,   386,   »248, 
391-393,   *249,   *251,   397,   *257, 
*258,  406. 

sensory  portion,  59,  97,  392. 

glosso-pharyngeal  (glosso-pharyngeus) , 
58,  '26ft,  *26c,  61,  84,  85,  87,  88, 
'237,  374,  376,  378,  383,  384, 
'244,  392,  '257,  403,  409. 

hypoglossal    (hypoglossus),  79,   '43,  84, 

85,  87,  '46,  94,  148,  251,  *163, 
260,  267,  '232,  '234,  »237-'240, 
373,  374,  376,  377,  '243,  383,  396, 
399,  '257,  403,  405,  406. 

oculo-motor  (oculo-motorius),  *18,  *67, 
*68,  *71,  115,  '76,  121,  122,  124, 
*80,  131,  '84,  '85,  '87,  *92,  '113- 
'115,  '141,  '183,  '191,  297,  '192, 
302-305,  *196-'199,  308,  309,  313, 
330,  '237,  374,  376,  389,  390, 
392,  '257,  410. 

olfactory  (olfactorius).  22,  47,  58,  145- 
148,  *98,  '99,  150-153,  *10o,  171, 
190,  '141,  213,  *142,  215,  217, 
218,  221,  236,  251,  '169,  274, 
407. 

optic  (opticus),  7,  17,  47,  *25,  56,  *37, 
*38,  84,  '63,  113,  '65,  '66,  115, 
116,  119,  '70-*74,  '81,  134,  136, 
139,  *87,  *88,  '91,  143,  '106, 
'110,  '112,  174,  '121,  '122,  188, 
'141,  213,  '144,  '158,  244,  251, 
'163,  254,  258,  '168,  267,  '176- 
'179,  280,  282-289,  '183.  '184, 
294,  '190,  '191,  297,  301,  304, 
'199,  308,  309,  407,  409,  410. 

pneumogastric  (vagus),  18,  58,  '266, 
'26c,  61,  64,  76,'39,»40c,  78, '42, 
84-90,  '46,  93,  95,  *52,  97,  '106, 
'107,  '235,  '237,  374-378,  '240, 
381,  '243,  383,  384.  '257,  409. 

spinal  accessory,  '43,  84,  85,  95,  '231, 
364,  3.65,  373,  374,  '237,  '257. 

trigeminal  (trifacial),  trigeminus,  59, 
*26ft.  *26c,  76,  *39,  79,  »43,  *44, 
84,  85, '46.  89,*50-»54,  95,  97,  98, 
105,  *65.  *71,  120,  *74,  '87,  '91, 
'92,  *106-*108,  '131.  '141,  '183, 
'199,  308,  '201ft.  '202,  '210,  330, 
364,  '233,  368,  '234,  374,  '239, 
376,  378,  382-384,  '245,  390, 
'248,  392-397,  *251-»253,  399, 
'257,  403,  408,  409. 

trochlear  (trochlearis),  *18,  56,  '56,  *60, 
108.  109,  *65.  115,  '76,  121,  •106, 
'113-'llo.  '141.  '182,  '183, '194, 
'196.  '199,  *201rt,  '2016,  313, 
328,  330,  '236,  '237,  '247,  389, 
390,  397,  '254.  '257. 

vestibular  (vestibularis),  *40D,  108.  386, 
'248,  390,  391,  409. 


438 


GENEEAL   IXDEX. 


Nerve,  electric,  66,  *48,  89. 

motor,  22,  23,  *7,  *11,  35-37,  *14,  57,  66, 

84,    338,    340,    351,    *258,    405, 

409. 
peripheral,  36-44,  *14,  *15,  *17,  55,  56,  62, 

332,  334. 
sensory,  22,  28,  *11,  35,  37,  *14,  *15,  40, 

*17,  57,  62-64,  *27,  85,  327,  328, 

332-334,  *214,  340,  348,  376,  407, 

408. 
spinal,  63,  64,  66,  81,  332-338,  *214,  *215a, 


217,  340,  348,  *228,  365,  *237. 


sympathetic,  37,  68,  85,  334. 
"tonus,"  93. 

Nerve-endings,  4,  36,  37,  39-42,  *17. 
Nerve-reticulum     (net- work),    cord,    spinal, 

16,  *17. 

bulb,  olfactory,  214. 
cortex  cerebri,  *151,  231-233. 
hypoglossal,  376,  377. 
regio  subthalamica,  272. 
Net  of  Gerlach,  20. 
Neuralgia,  330. 

Neuraxon,  20-25,  28,  29,  *11,  33,  36,  37,  *15, 
*16,  58,  62,  63,  66,  68,  80,  87,  89,  ! 
93,  95,   104,   110,   116,   146,   147, , 
168,  213,  214,  227,  228,  231,  233, 
236,  287,  308,  311,  313,  320. 
Neurite,  20-22,  *11,  *15,  69,  73,  331. 
Neuroblast,  16,  17,  78,  168. 
Neuroglia,  *4-*6,   17,  30,  227,  236,  237,  239, 
*208,  319,  328,  329,  343,  344,  363, 
380. 
Neuron,  23,  31,  36,  69,  139,  146,  147,  151,  213,  ! 

215,  320,  368,  387,  388,  406,  407. 
Nodulus  cerebelli,  *204,  317,  319. 
Nucleus,  see  also  ganglion, 
ambiguus,  375,  *243,  *257. 
amygdala?.  149,  *127,  190,  215,  *162,  269, 

'*174,  *178. 

aqueduct  of  Sylvius,  floor,  *196,  303. 
arcuatus  (arciformis),  83,  98,  378,  379. 
Bechterew's  391. 

caudatus,  54,  *104,  157,  *125,  187-190,  *127, 
*144,  *154,  240,  245,  *160-*163, 
249,     250,     *165-*169,     256-258, 
*171,  *172,  266,  267,  269,  *174-  ; 
*179,  278,  *185,  *186,  406. 
cen tralis,  interbrain,  *169. 
cerebelli,  92,  319-323. 

dentatus,  106,  323,  326,  381,  *245. 
globosus,  *47,  106,  322,  323,  *209. 
tegmenti  (fastigii),  323,  b26,  *209,  *211, 

*212. 

commissuralis  nervi  vagi,  376. 
corporis  candicantis,  274. 
geniculati  lateralis,  260,  261. 
quadrigemini  posterioris,  300,  301. 
Deiter's,  *47.  93,  99,   108,  *211,  328,  351, 

*248.  391. 

entopeduncularis,  134. 
epithalami,  129. 

fasciculi    longitudinalis     posterioris,     122,  j 
123,  *83,  136,  137,  *115,  177-179, 
278,  *191,  305. 


Nucleus  of  fillet    (lemniscus),  lateral  or  in- 
ferior, »191,  388,  398. 
median,  398. 
funiculi  solitarii,  392. 

teretis,  376. 

interbrain,  134,  136,  *169,  278. 
laquearis,  *50,  *201o,  *2016,  313,  *247;  see 

also  nucleus  of  fillet. 

lenticularis  (lentiformis),  3,  54,  *84,  144, 
157,  *127,  189,  190,  242,  245,  246, 
*160,  250,  *162,  *163,  *165,  255- 
257,  *166,  *168,  263,  267,  269, 
271,  *176,  277,  *185,  308,  406, 
408. 

medialis  of  Meynert,  376. 
nerves,  cranial,  *26&,  *26c,  75-100,  304,  374- 

376,  383,  *257,  402-409. 
abducens,  *47,  *49,  95,  *115,  304,  *247, 

389,  390,  *248,  392,  *257. 
auditory   (acusticus),  58,  76,  *39,  *40D, 

*46,  *48,  91,  92,  *49,  93,  94,  105, 
*60,  108,  245,  251,  285,  *257. 
dorsal,  93,  384,  385,  *244,   "245,  *248, 

390,  391,  409;    see  also  nucleus 
nervi  vestibuli. 

ventral,  93,  *54,  *244,  385,  *245,  386- 
388,   *247,   *248,   391,  409;     see 
also  nucleus  nervi  cochleae, 
cochlear,  387,  388. 

facial,  *266,*26c,  61,  79,  *46,  *47,  *49,  *50, 
95,  *54,  97,  374,  376,  384,  *244, 
391-393,  *251,  397,  *257,  406. 
glosso-pharyngeal,  *266,  "26c,  *46,  88, 
*47,  376,  378,  383,  *244,  392, 
*257,  403,  409. 

hypoglossal,  *46,  260,  *234,  *238,  374, 
376,  *240,  377,  *243,  383,  396, 
399,  *257,  403,  405,  406. 
oculo-motor,  *67,  *68,  121,  122,  *80,  *85, 
*115,  302-305,  *196,  *197,  308, 
309,  *257. 

pneumogastric  (vagus),  76,  *39,  *40c.  79, 
*42,  86,  *46,  89,  *235,  375-378, 
*240,  *243,  383,  384,  *257,  409. 
motor.  87,  89,  90,  *52,  374,  375,  *239, 

383,  384. 

sensory,  86,  88,  374,  375,  383,  384. 
terminal,  85,  86. 
spinal  accessory,  *257. 
trigeminal,  76,  *39,  79,  89,  *51,  95,  97, 
*54,  98,  105,  *65,  308,  383,  *251, 
396,  *252,  397,  408.  409. 
motor,  *50,  *65,  393,  394,  *251,  *252, 

*257,  403,  409. 
sensory,  *50,  95,  97.  394. 
terminal,  79,  *43,  85,  *46,  97,  *91,  364, 

394,  *251,  *257. 
trochlearis,  121,  *115,  *196,  *199,  *201a. 

*201ft,  313,  *257. 
vestibularis,  391. 

nervorum  electricorum,  *29,  *31,  66,  89. 
of  Luys,  272. 
of  medulla,  18,  72,  84.  98. 

euneatus.    *232,    *233,    367,    368,    *235, 
*239,  *243. 


GENERAL    INDEX. 


439 


Nucleus,  of  medulla,  gracilis,  *231,  *233,  367. 

368,  *235,  *239.  *243. 
lateralis,  366,  *239. 
motor,  402,  407. 

posterior,  or  dorsal,  79,  *41,  81,  *43,  85, 
98,   108,   118,  272,  368,  370-372, 
*238,  382-384,  397,  399,  408. 
raphe,  *46,  *47. 
sensory,  143,  398,  399. 
of  midbrain,  base,  115,  120. 

profundus  lateralis,  *71,  121,  123,  *73. 

medialis,  123,  *73. 
roof,  98,  120. 
olivaris,  see  oliva. 
pons,  311. 

praetectalis,  114,  *71,  *72,  133,  *83,  134. 
region,  subthalamic,  277. 
reticularis  tegmenti,  366,  384,  393,  400. 
Roller's  hypoglossal,  *240,  377. 
ruber  tegmenti   (red  nucleus),  56,  99,  122, 
*83,   137,   145,   *175,  272,   *179, 
278,    284,    *192-*194,    299,    306, 
*198,   *199,   308,   310,   312,   314, 
315,  326,  381,  401. 
stratum  intermedium,  274. 
tseniee,  *98,  *99,  152. 
tegmenti,  see  nucleus  ruber  tegmenti. 
thalami,   134,   136,   157,  244,  258-260,  263, 

289 :    see  also  ganglion, 
anterior,   *70,   132,   *83,   188,   *144,  259, 
•169,  267-269,  *173,  *174,  *176, 
275,  277,  *178,  278. 
diffusus,  132,  133. 
lateralis,  *125,  259,  *169,  267,  268,  *173- 

*179,  277,  278. 
layer,  latticed,  260. 
magno-cellularis,  72,  132,  *82,  260. 
medius,    132,    133,   *82,    *125,   259,   260, 
*169,   268,   *174-*179,   277,   278. 
rotundus,  *81,  132,  *82-*86,  *91,  *95. 
ventralis,  136,  259,  260,  263,  *175,  272, 
276-278,   *178,   *179,  290,   *191, 
397-399. 

trapezoideus,  387. 
Nystagmus,  329. 

Obliquus  inferior,  304. 
Oculo-motorius,  see  nerve,  oculo-motor. 
Olfactorius,  see  nerve,  olfactory. 
Oliva,  see  also  body,  olivary, 
accessory,  anterior,  383. 

posterior,  *234,  383. 
cerebelli,  106. 

inferior,  3,  *46,  108,  *183,  328,  363,  366, 
*233-*235,  368,  371,  *237,  373, 
*239,  377,  379-381,  *241-*244, 
383,  384,  *257. 

superior,  *48,  93,  96,  53,  *98,  108,  *245, 
387-389,  *247,  *248,  391,  392, 
409. 

Ontogeny  of  central  nervous  system,  33. 
cerebellum.  103. 
fissure,  203. 

fundaments  of  cranial  nerves,  58. 
medulla,  100. 


Ontogeny,  nerves,  sensory,  37. 

Operculum,   *23,    192,   *130,    194,   «131     259 

295. 

Ophthalmoplegia,  330,  331. 
Opisthotonos,  331. 
Opticus,  see  nerve,  optic. 
Organ  of  Corti,  40,  *16. 

electric,  20,  66,  90. 

equilibrium,  94. 

parietal,  *25,  *110;  see  epiphysis,  or  cona- 
rium. 

sense,  special,  15. 
Otocyst,  *266,  »26c,  61. 
Otolith,  function,  39. 

Pain,  lesions  of  spinal  ganglia,  334. 
Pallium,  50,  *25,  56,  *37,  *74,  »76,  *80,  *86, 
*95,    145,    *101,    159-179,    »107, 
*109-»112,   »122,  211,   213;     see 
also  mantle. 
Papillae,  sensory,  43. 
Paralysis,  360,  362,  402. 
abducens,  402. 
crossed,  330,  403. 
facial,  402. 

oculo-motor,  302,  309. 
progressive,  260,  322,  328. 
spinal  infantile,  407. 
Paraphysis,  *18,  49,  *25,  127,  *76,  *86,  *95 

*110,  *114. 

Paresis  in  amyotrophic  lateral  sclerosis,  361. 
Pars  caudalis,  internal  capsule,  *177. 
commissuralis,  midbrain,  118. 
corticalis,  olfactory  apparatus,  *101. 
epistriatica,  *101. 
dorsalis  ganglii  isthmi,  *60. 
olfactoria,  *25,  *101,  *108,  *110,  *176. 
opercularis,  194. 
Path,  see  tract 

Patheticus,  see  nerve,  trochlear. 
Pectoralis  major,  spinal  center,  336. 
Pedicle,  commissura  anterior,  216. 
corpus  geniculatum,  *177,  288,  290,  *191. 
conarii  (epiphysis.  glandula  pinealis),  *125. 

188,  276. 
habenulae,  *44. 

thalamus,  inferior.   *159,  240,   *168,  *174, 
*175,  *177,  *179,  263,  267,  269, 
280,  *191. 
Peduncle  (pedunculus). 

cerebellar,  *91,  107,  "65.  122,  *84,  245,  317- 
319,  *205,  323-327,  *211,  329, 
330,  350,  393,  407. 

anterior  or  superior,  106,  107,  *61,  *65, 
122,  *84,  137,  272,  283,  284,  »182, 
•183,  299,  »193,  308,  310,  312, 
*201a,  *201&,  314-318,  *202-*205, 
'209,  324,  »210,  326,  *212,  328, 
*236,  373,  381,  '253,  399-401, 
*254-*256. 
inferior,  99,  108,  *61,  299,  315,  "205,  326- 

329,  373,  379,  380,  382. 
middle,  108,  *61,  315,  *205,  324;    see  also 
brachium  pontis. 


440 


GEXEKAL    INDEX. 


Peduncle,  cerebral,   3,   124,   188,   *135,   *141, 

*144,  *158,  *180,  *182,  283,  *185, 

*187,  *197,  306,  309,  311,  *236; 

see  also  crus  cerebri. 

corpus  mamillare,    *144,   *176,   *177,   274, 

*199,  309,  312. 
quadrigeminum,  143. 
decussatio  supra-infundibularis,  *90. 
flocculi,  317. 
Perception,  43,  357. 
Peristalsis,  36. 
Peronei,  spinal  center,  337. 
Pes,  gyrus,  frontal,  third,  194,  *172. 
hippocampi,  199. 

inferior,  sulcus  prcecentralis,  *130,  *131. 
pedunculi,  *112,   *141,  211,  *158,  254-256, 
*165,    263,    *175.    272,    176-179, 
276,    278-280,    282,    *183,    *185, 
*186,    290,    291,    294-296,    *191, 
*192,  298,  299,  *195,  *198,  *1G9, 
308-312,   *200,   *201a,   324,   326, 
344,   366,    367,    *237,    374,    376, 
*251,  *258,  401,  403,  405-407. 
Pharynx,  43,  281. 

Phylogeny,  apparatus,  olfactory,  211. 
central  nervous  system,  32,  33. 
cerebellum,  102,  103. 
cortex  cerebri,  145,  174,  209. 
mantle,  177,  179,  211. 
mechanism,  optic,  174,  175. 
medulla,  100. 
midbrain,  124. 

Physiology,  apparatus,  olfactory,  158. 
cord,  spinal,  357,  360. 
corpus  quadrigeminum,  285. 

striatum,  158. 
cortex  cerebri,  173,  174,  179,  205,  208-211, 

226. 

fillet,  299,  300. 
ganglia,  26. 
hypophysis,  281. 
medulla,  402-405. 
pons,  402-405. 

thalamus  opticus,  259,  261,  262. 
Pia  mater,  319. 

Pillar  of  fornix,  187-190,  218,  *144,  242-249, 
250,    *162,   267,   274,   279;     see 
also  columnar  fornicis. 
Pit,  auditory,  57,  58. 
nasal,  57,  58. 
olfactory,  57. 
oral,  57. 

Plate,  cerebellar,  101-105,  *56,  *57,  110. 
corpus  quadrigeminum,  *20. 
cribriform,  146,  213. 
electric,  90. 

end  motor,  21,  23,  24,  90. 
medullary,  15,  49,  57. 
midbrain-roof,  115,  117,  *197. 
Plate-cells,  neuroglia,  17,  237. 
Plexus,  brachial,  340. 
cervical,  334. 

chorioideus,  53,  *25,  56,  126,  *76,  127,  *110, 
*114,  *115,  167,  171,  *120,  187, 
199,  201,  *154,  276,  279. 


Plexus  chorioideus.  anterior.  289. 
lateralis,  52,  319. 
ventriculi  lateralis,  *154,  *172,  268. 

quarti,  101,  319,  *243. 
lumbar,  334. 
nerves,  peripheral,  334. 
subcorticalis,  168. 
Polus    (pole)    frontalis,   162,   163,   *113,   176, 

264,  266. 

occipitalis  pallii,  162,  163,  193. 
temporalis,  162,  *113. 
Poliomyelitis  acuta,  362. 
Pollex,  cortical  center,  *148. 
[  Pons,  5,  50,  *20,  *37,  102,  108,  *112,  211,  *141, 
*144,   242,   243,  245,   250,   *163, 
252,    254,    264,    269,    280,    *180, 
*182,  *183,  *187,  *190,  299.  *194, 
*197,    308,    310-312,    *200-*202, 
314,    315,    317,    *204-*206,    324, 
*211,   326,   *212,   329,   330,   344, 

364,  366,  367,  *234,  *236,  *237, 
373,  374,  376,  379,  384-400,  *245, 
*247,  *248,  *252-*258,  401-409. 

Portio  intermedia  Wrisbergi,  392. 
Portio  major  nervi  trigemini,  397. 

minor,  393. 

Prsecuneus,  *133,  198,  *188,  *189. 
Pressure-sensation,  spinal  tract,  357. 
Processus  reticularis,  81,  83,  *216,  338,  *230, 

365,  366. 

superior  vermiform,  316,  318,  328. 

Pronators,  spinal  center,  336. 

Prosencephalon,  49,  50,  52,  56;    see  forebrain. 

Psalterium,  177,  *123,  186,  217,  *143,  218, 
*144,  220,  242,  *165,  *169,  *175- 
*177,  *179,  279,  *185,  291,  *191; 
see  also  lyra  Davidis. 

Psychology,  comparative,  174,  175,  179. 

Ptosis,  309. 

Pulvinar  thalami,  188,  *165,  259,  260,  *177, 
*180,  282,  *182,  285,  *183,  286- 
289,  *185,  291,  297,  *191,  298, 
*195,  *198,  *236,  409. 

Pupil,  309. 

Putamen  nuclei  lentiformis,  157,  *121,  *125, 
190,  250,  256,  257,  *167,  *169, 
*171-*174,  266,  267,  270,  278, 
*176. 

Pyramids,  3,  83,  280,  *190,  330,  334,  *231- 
*234,  366,  367.  369,  *236,  *237, 
370,  373,  377,  379,  *241,  382,  383, 
*244-*246,  *248,  *252,  401,  402; 
see  also  tract,  pyramidal. 

Pyramis  cerebelli,  317,  *204. 

Quadriceps  femoris,  spinal  center,  337. 

Rachitis,  207. 

Eadiation  (radiatio),  auditory,  245. 

coronal,  210. 

corpus  callosum,  242,  *158. 

cortico-spinal,  246. 

cortico-thalamica,  *163. 

fasciculi  fronto-occipitalis,  242,  265. 


GENEEAL   INDEX. 


441 


Radiation,  fillet,  superior,  272. 
occipito-temporalis,  290. 
occipito-thalamica,    240,    *165.    *185-*189, 

293. 
olfactory,  201,  215,   217,   *144,  221,   *169, 

267,  282. 

optic,  244,  245,  *160,  259,  *177,  285,  *183, 
288,  290-294,  *191,  308,  408,  410. 
putamen,  267. 

regio  subthalamica,  272,  273. 
strio-thalamica,  *166,  257,  261,  266. 
tegmental,  245,  251,  253,   254,   257,   *167, 
272,   278,   *190,  299,   *193,   315, 
408. 

temporo-thalamica,  *165,  *185. 
thalamic,  259,  260,  263,  *176,  *177. 
thalamo-occipitalis,  288,  290. 
Radix  (root). 

nerves,  cranial,  77,  84,  85,  89,  146,  406,  407. 
abducent,  94,  392. 
auditory,  *245. 
anterior,  *49. 

descendens,  *49,  *53,  *54,  384,  391. 
posterior,  *49,  92. 
facialis,   *26b,   *26c,   84,   95,   *244,   *245, 

*248,  392,  393. 
glosso-pharyngeal,  91,  375. 

spinalis,  *43,  88,  375,  376. 
hypoglossal,  94,  *238,  374. 
oculo-motor,  *191,  302. 
olfactory,  *86,  146,   148,  *95,  *118,  215, 

283. 

optic,  *69,  *82,  139,  143,  287. 
pneumogastric   (vagus),  *266,  *26c,  *52, 

*243,  391. 

bulbo-spinalis,  88,  376. 
motor,  79,  *46,  95,  *52,  375. 
sensory,  87,  375,  *243,  382. 
trigeminal,    *26ft,    *26c,    *43,    84.    308, 
*2016,  *210,  364,  368,  *252,  397. 
mesencephalic,  97,  *59,  120,  308,  *201&, 

364,  393,  394,  *252,  *253,  399. 
motor,  293,  *251. 
sensory,  *251. 

spinal,  79,  *43.  85,  *46,  88,  95,  *52,  99, 
*71,  *199,  308,  *202,  364,  *233, 
368,   *239,   382-384,    *245,   *248, 
390-394,  408,  409. 
vago-glosso-pharyngeal,  383. 
vestibular,  *248. 
nerves,  spinal. 

anterior,  or  ventral,  *13,  37,  63,  *28-*31, 
*33,  66,  68-70,  73,  *41,  84,  146, 
*213-*216,  332-334,  338,  *218, 
344,  351,  357,  358,  *229,  *230, 
*257,  407. 

posterior,  or  dorsal,  *13,  57,  62,  63,  *27- 
*31,   *33,   66,   68,   *41,   81,   146, 
*213-*216,  332-334,  340.  341,  344, 
348,    349,    *227,    351-356,    358- 
360,  364,  *235,  407. 
thalami,  *64,  134. 
Ramifications,  arborescences,  22-24,  28-30,  63, 

68,  69,  116. 
Ramus  buccalis,  61. 


Ramus  cochlearis  nervi  acustici,  *16. 
lateralis  vagi,  *26&. 
marginalis  sulci  cinguli,  *133,  *170. 
subparietalis  sulci  cinguli,  *133. 
Raphe,  medulla,  80,  81,  *46,  *47,   109,  382, 

383,  388,  406. 
plate,  medullary,  49. 
pons,  *201o,  311,  393,  399,  400. 
tegmentum,  403. 
Rays    (radii),  cortex  cerebri,  229,  232,  233, 

236,  244. 

Respiration,  lesions  of  medulla,  402,  405. 
Reticulum,   tangential,    168;     see   also   net- 
work. 
Retina,  40,  139,  261,  287,  294,  409. 

of  epiphysis.  127. 

Recessus  inferior,  *25,  *76,  *110,  *114. 
infundibularis,  56,  *141. 
mamillaris,  *25,  *76,  *77,   129,  *90,  *108, 

*110,  *114,  '141,  *176. 
opticus,  *25,  *110,  *141. 
prseopticus,  *76,  128,  *114. 
postopticus,  128. 

Rectus  inferior,  innervation,  304. 
internus,  304. 
superior,  304. 

Reflexes,  70,  71,  355,  356,  358. 
abdominal,  337. 
cremasteric,  337. 
epigastric,  337. 
gluteal,  337. 
motor,  theory  of,  358. 
palmar,  336. 
patellar,  337. 
plantar,  337. 
pupillary,  336. 
rectal,  337. 
scapular,  336. 

sensory-motor,  of  face,  397. 
tendo  Achillis,  337. 
vesical,  337. 

Reflex-action,  31,  *  11,  32,  35,  36,  43,  70.    , 
Reflex-centers,  35,  36,  44,  336,  337. 
Reflex-paths  or  arcs,  35,  36,  41,  43,  69. 
Regio  insulae,  *156. 
parolfactoria,  167. 

subthalamica.    257,    271-279,    *172,    »175, 
*177,  *179,  280,  *191,  309,  310. 
Rhinencephalon,  145,  216. 
Rhombencephalon,  *18. 
Rhomboidei,  spinal  center,  336. 
Rima  glottidis,  *149. 
Roof,  cerebellum,  69,  101. 
metencephalon,  310,  317,  318. 
midbrain     (mesencephalon),    72,    112-115, 
»65,  *66,  117,  118,  121,  189,  290, 
295,  300-302,  *195,  308,  318,  401. 
thalamencephalon,  51,  56,  276. 
ventricle,  fourth,  315,  319,  372,  373. 
Roof-nucleus,  cerebellum,  92. 

midbrain,  98,  120. 
Root,  see  radix. 

Root-zone,  cord,  spinal,  *223,  354. 
Rostrum,  corpus  callosum,  *171,  266. 
Rotators  of  thigh,  spinal  center,  337. 


442 


GENERAL   INDEX. 


Sac,  epiphyseal,  129. 

Saccule,  ear,  91. 

Saccus  vasculosus,  *18,  *77,  129,  *90,  *108. 

Sartorius,  spinal  center,  337. 

Scaleni,  spinal  center,  336. 

Schema,   association-pathways,   hemispheres, 

*156. 

bulb,  olfactory,  *142. 
capsula  interna,  *163. 
commissure  of  olfactory  apparatus,  *101, 

153. 

convolutions,  base  of  brain,  *135. 
cord,  spinal,  *28,  *213,  *227,  368,  *235. 
corona  radiata,  fibers,  *159. 
corpus  striatum,  *98. 
cortex,  motor  centers,  *148,  *149. 
ganglion,  spinal,  fibers,  *214. 
interbrain,  nuclei  and  tracts,  *83. 
muscle,  innervation,  *229. 
nerve,  abducens,  *249. 
cochlear,  *247. 
facial,  *249,  *258. 
motor,  *11,  *258. 
peripheral,  *14. 
sensory,  *11,  39,  *15,  *28. 
trigeminal,  394,  *251. 
nerve-tracts,  *14. 
peduncles,  cerebellar,  *211. 
reflex-action,  *11. 

system,  olfactory,  *98,  *100,  «101,  *144. 
Sclerosis,  amyotrophic  lateral,  361,  362. 
Secretion,  regulation  of,  43. 
Sections,  frozen,  4. 
Sense,  muscular,  269,  360,  403. 
Sensibility,  44,  225,  362. 
Senso-mobility,  43. 
Sense-organs,  15,  21,  40,  57. 
Septa,  cord,  343,  347. 

Septum  pellucidum,  *22,  53,  *24,  *76,  *114, 
*115,  165-167,  171,  172,  *120, 
175,  *123,  *125,  *126,  *132,  *133, 
*144,  186,  190,  196,  197,  201, 
215,  217,  220,  249,  *171,  266, 
267. 

Sermo,  cortical  center,  *148. 
Serratus  magnus,  spinal  center,  336. 
Sheath,  medullary,  of  nerves,  9,  *10,  30,  55, 

231,  233,  306,  342,  344. 
of  Schwann,  30,  342. 
Sight,  center,  245. 

disturbance  of,  294. 

Sinus  (fossa)  rhomboidalis,  73;    see  also  ven- 
tricle, fourth. 
Skin,  heat-loss,  43. 
innervation  by  pneumogastric,  86. 

spinal  nerves,  336,  337. 
nerve-endings,  sensory.  41. 
Smell,  center,  cortical,  171,  218,  226. 

sense  of,  158,  174,  209,  251. 
Spasticity  of  muscles,  361,  362. 
Spatium  olfactorium,  *141,  *143,  *144. 
Speech,  cortical  center,  *148,  240,  247,  267, 

406. 

disturbance  of,  330,  402,  405,  406. 
nuclei,  medulla,  245. 


Speech-tract,  245,  246,  253,  *171,  *173,  267, 

269,  403,  406,  407. 
Sphincter  iridis.  304. 

|  Spinal  accessory,  see  nerve,  spinal  accessory. 
Splenium,  corpus  callosum,  197,  *158,  *186, 

292. 

Spongioblasts,  16,  17. 
Staining,  vital,  5,  13,  21,  *8. 
Sterno-mastoid,  spinal  center,  336. 
Stiff  neck,  331. 

Stilus  corpus  geniculatum,  133,  136. 
Stratum    complexum   et   profundum   pontis, 

•  311. 
intermedium,  255,  272,  274,  *191,  299,  *199, 

308,  314. 

lemnisci,  299,  300,  *194,  308,  313,  315. 
lucidum,  gyrus  hippocampi,  *154,  236. 
medullare  profundum,  midbrain,  *66,  116- 
118,  *68,  143,  290,  300-302,  *194, 
*199;    see  also  layer,  deep  med- 
ullary. 

opticum,  *67. 

oriens,  gyrus  hippocampi,  *154,  236. 
radiatum,    gyrus    hippocampi,    235,    *154, 

236. 

superficiale  pontis,  311. 
zonale  thalami,   188,  258,  259,  *168,  *169, 
268,   269,   *176,   *177,   285,   290, 
*191. 
Stria   acustica,    *182,    *205,    *236,   374,   378, 

*244,  *245,  387,  388,  *247,  409. 
cornea,  190. 

longitudinalis  Lancisi,  *124,  200,  216. 
medialis,  *124,  220,  "171,  *172,  *176. 
medullaris  thalami,  312,  314. 
externa,  263,  272. 
interna,  263. 

terminalis,  *125,  188,  267,  269. 
Structure,  cortex  cerebri,  145,  *116,  167,  168, 

*117,  227,  235,  236. 
ganglion,  spinal,  62. 
ganglion-cells,  20,  24,  25. 
glandula  pinealis,  epiphysis,  276. 
hypophysis,  280,  281. 
olive,  accessory,  283. 
tegmentum.  312. 
Subiculum,  2l6,  234,  *154. 
Subnuclei  of  thalamus,  260. 
Subscapularis,  spinal  center,  336. 
Substantia  cinerea  centralis,  *127,  *162. 
gelatinosa  Rolandi.  79,  *49,  341,  *219,  343, 
*223,  355,  *231,  364,  *233,  368, 
374,  *243,  383,  384,  *245,  *248. 
394,  *252. 
gray,  central,  of  aqueduct,  278,  295,  *194, 

301,  *199,  312,  313,  315. 
cord,  spinal.  63,  64,  66,  68,  70,  71,  243, 

337,  338,  341,  343,  352. 
ectoventricular,  265. 
medulla,  75,  78,  79. 
midbrain,  121,  *73. 
thalamus,  132,  *91,  188. 
ventricle,  third,  138,  190,  260,  *168,  267, 

*173,  274.  278,  294. 
lateral,  264,  265. 


GENERAL   INDEX. 


443 


Substantia  innominata,  *168,  263,  280. 

medullary    (white),   cerebellum.   318,   319, 

323,  324. 

cerebrum,  265,  267,  277,  290,  295,  318. 
cord,  spinal,  63,  70,  73,  337. 
vermis  cerebelli,  324. 

nigra,  midbrain,  123,  255,  257,  *165,  *166, 
*175,  272,  274,  *177,  276,  *179, 
278,  *185,  296,  *191,  *192,  299, 
*195,  *198,  *199,  308,  314,  398, 
401. 
perforate  anterior.  *161,  *180,  282,  283. 

posterior,  *177,  279,  280. 
reticularis,  314,  315,  *233,  *234,  381,  *243, 

384,  397. 

pontis,  *202,  314,  315,  393,    253,  399. 
tegmenti,  400. 

tracti  thalamo-bulbaris,  *201a. 
Subthalamus,  *175. 
Sulcus,  see  also  fissure, 
arcuatus,  221. 
centralis,  *129-*131,  193,  221. 

insulae,  193. 
cerebral,  164,  192. 

cinguli,  *133,  197,  198,  216,  "170,  "188. 
frontalis  inferior,  *130,  194,  *131. 

superior,  *130,  194,  *131. 
intermedius   posterior,   cord,   spinal,   *215, 

*216. 

interparietalis,  *130,  *131,  194,  195. 
island  of  Reil,  191. 
occipitalis  anterior,  *130,  *131,  195,  196. 

lateralis,  *130,  *131. 
olfactorius,  201,  *135. 
orbitalis,  201,  "135. 
parieto-occipital,  *130,  *131. 
pnecentralis,  *130,  *131,  194. 
retrocentralis,  *130,  *131. 
sagittal,  221. 

temporalis,  *130,  *131,  194,  *135,  222. 
inferior,  201. 
superior,  195. 
variations,   221. 
Supinator  brevis,  spinal  center,  336. 

longus,  336. 

Supraspinatus,  spinal  center,  336. 
Surface,  cerebellum,  literature,  329. 

hemispheres,  191-207. 
Swallowing,  reflexes,  43. 
Sympatheticus,  85. 
Symptomatology,  lesions  of  cerebellum,  329, 

330. 

of  medulla  and  pons,  402-405. 
Syringomyelia,  362. 
System,  motor,  of  cord,  68. 
olfactory,  *98,  *100,  *101. 
optic,  146,  261. 
peripheral  nervous,  15,  37. 
sympathetic,  33,  35,  37,  41,  334. 
tegmental,   124. 
System-diseases,  cord,  7. 

Tabes  dorsalis,  334,  348,  357,  362. 
Table  of  Starr,  innervation  of  ocular  mus- 
cles, 304. 


Taenia  habenulse,  276. 

semicircularis,  188,  *169,  *174. 
thalami,  131,  *82,  *98,  *99,  152,  *100,  *120, 
*125,  188,  *144,  220,  221,  "169, 
*174-*179,    267,    268,    276,    277, 
306. 
Tail,  nucleus  caudatus,  249,  258,  269,  278, 

406. 
|  Tapetum,  241,  242,  *158,  267,  *i86-"188,  292 

293. 
I  Taste-center,  40,  *48,  378. 

tract,  403,  409. 
Tectum  opticum,  *18,  71,  98. 
mesencephali  (midbrain),  *38,  *56,  63,  *64, 
114,  *67,  "69,  "70,  120,  "79,  "81, 
"83,  "86,  "88,  "89,  "91,  143,  "95, 
"97,  "121;    see  also  roof. 
Tegmentum,  medulla,  313. 

midbrain,  56,  93,  117,  118,  "73,  123,  "112, 
197,  254,  257,  "168,  272,  "176, 
"177,  275,  276,  278,  284,  "183, 
"186,  290,  295-309,  "190,  "192 
"199,  310,  312,  "201,  313,  315 
324,  326,  381,  383,  384,  392,  393, 
400,  401,  403. 

pons,  311,  312,  "2016,  328,  385-400,  403,  406. 
;  Tela  chorioidea  anterior,  "75,  127,  "79,  "82 

"86,  "92,  "95,  145,  "99,  151. 
posterior,  *37,  75,  "39,  78. 
I  Telencephalon,  "18,  "64,  "72,  "83,  "84,  "92. 
I  Temperature,  disturbance  of  sense  of,  362. 

impressions,  path,  357. 
Tendon-reflexes,  43,  336,  337,  360. 
Tentorium,  293,  330. 

Teres,  major  and  minor,  spinal  center,  336. 
Thalamencephalon    (interbrafn)    50-52,    "24, 
56,   82,   98,    125-144,   310,   "236, 
402. 

Thalamus  opticus,  "19,  "20,  51,  56,  114,  119, 
121,  122,  125-144,  "74,  "75,  "80, 
"81,  "82,  "84,  *90-"93,  "99,  154, 
156,  157,  169,  "120,  "122,  176,  178, 
"125,  186-190,  "127,  196,  "133, 
200,  218,  "144,  220,  240,  243, 
"158,  244,  245,  *159-"163,  248- 
250,  252,  254,  "165,  "166,  257- 
272,  "168,  "169,  "173-M79,  274- 
280,  282-285,  "182,  "183,  288-290, 
"185,  293-297,  "190,  "191,  299, 
"193,  "195,  "198,  306-309,  "199, 
*201fl,  312,  314,  315,  326, 
"236,  389,  390,  398,  399,  408, 
409. 
Thumb,  center,  "148. 

innervation,  67. 

Tibialis  anticus,  spinal  center,  337. 
Tongue,  cortical  center,  "149. 
Tonsilla  cerebelli,  317,  "204,  318. 
Tonus,  muscular,  44,  91,  102,  110,  381. 

nerves,  93,  102. 

Torus  semicircularis,  121,  "85,  302. 
Touch-sense,  judgment,  226. 
Tract  (tractus),  general  considerations,  6,  7, 

bulbo-corticalis,  "94,  150,  "98,  "100,  215. 


444 


GENEKAL    INDEX. 


Tract,  bulbo-epistriaticus,  *94,  149,  *97,  150, 

*98,  *100,  169. 
capsule  internal,  252,  267. 
cerebellum,  83,  99,  101,  106,  107,  111,  *217, 

368. 
cerebello-nuclearis,  *211. 

olivaris,   108,  *211,  328,  380,  *242,  381- 

384. 

spinalis,  71,  *35a,  *40c,  *41,  81,  *43,  *46, 
*49,  99,  *60,  108,  *61,  110,  *71, 
•211,  328. 

dorsalis,  328,  *225,  349,  350,  *234. 
ventralis,  328,  *225,  349,  350,  *234. 
tegmentalis,  109,  311. 
cerebrum,  99,  101,  145,  184,  258,  259,  309, 

311. 
cortical,  33,  243-247,  254,  255,  258,  259, 

261. 

intralobular,  240. 
cord,  spinal,  70,  71,  98,  134,  211,  246,  326, 

337,  351-357,  359. 
anterior,  70. 

antero-lateral,  71,  350,  357,  383. 
association,  354. 
cerebellar,  direct  sensory,   92,  327,  328, 
349,    350,    357,    *233,    378,    379, 
*241,   *243-*245,   384,   391,   393, 
*252,  397,  408. 

cervico-lumbalis   dorsalis,   354. 
intermedio-lateralis,  *216,  338. 
lateral,  70,  302,  328,  349,  363,  366,  408. 
posterior,  62-66,  68,  76,  *28,  71,  85,  346, 

352-357,  362,  368. 
pressure-sensation,  357. 
pyramidal,  72,  83,  246,  251,  253,  254,  267, 
*190,  *192,  298,  299,  *199,  *200, 
308-311,  344-346,  *221-*223,  349- 
353,  360-362,  *231,  366-368,  373, 
*239,   377,   379,  382,   *243,   385, 
399,  405,  406. 
crossed,  8,  72,  225,  226,  *223,  349,  351, 

366,  405. 
direct,  *223,  *225,  351,  352,  358,  366, 

405. 

Schulfcze's   (comma-tract),  354. 
tactile  impressions,  357. 
temperature-sensations,  357. 
corticis  ad  pontem,  245. 
cortico-bulbaris,  245,  246. 
epistriaticus,  *97,  151. 
habenularis,  131,  172. 
mamillaris,  *100,  172. 
olfactorius,  151,  MOO. 
septi,  *100,  201,  217. 
pontile,  311,  326,  336. 
spinalis  (pyramidal).  72,  83,  99,  246,  299, 

344-346,  *221,  352,  361,  366. 
tegmentalis,  272. 
thalamicus,  134,  135,  144,  176,  244,  246, 

252,  *163,  *272. 
crural,  pons,  401. 
fillet,  244,  300. 
frontal  to  pons,  254.  269. 
fronto-occipitalis,  242. 
dorsalis,  *104. 


Tract,  fronto-thalamicus,  *83,  134,  243. 
gustatory,  403. 

habenulo-peduncularis.  *44,  *64,  *80,  131, 
*81,  132,  *83,  *93,  *100,  276, 
306. 

hearing,  253. 
hemisphere,    association-tracts,    240,    246, 

277. 

interbrain,  98,  99,  101,  130,  *83,  134. 
intratectal,  associational,   114. 
lobi  inferioris  ad  cerebellum,  68. 
lobo-cerebellaris,  *91. 

frontalis,  *85. 
mamillo-peduncularis,  *83,  *201a. 

tegmentalis,  277. 
medulla  oblongata,  77,  83,  98,  99,  101    368 

372. 

ad  nucleum  funiculi  posterioris,  *211. 
associatus  brevis,  80,  *41,  *46,  *52-*54. 
interolivary,  *234,  403. 
lateral,  *244. 
postero-lateral,  367. 

median,  367. 
tactile,  cutaneous,  403. 
midbrain,  47,  81,  99,  114,  134,  245,  260,  295. 
motor,  *163,  402. 
nerves,  cranial,  399,  402-408. 
auditory,  93,  109.  403. 

acustico-cerebellaris,  *47,  327,  328. 
spinal,  82,  93,  94. 
tectal,  *46,  *48,  93. 

dorsal,  *48,  *49,  93,  *54. 
ventral,  *48,  93,  96,  *53. 
central,  408,  409. 
cortical,  408. 
secondary,  388. 
tecto-acusticus,   *71. 

spinalis  acusticus,  *50. 
facial,  267,  406. 
glosso-pharyngeal,  spinal,  *46. 
hypoglossal,  267,  406. 

central,  245. 

olfactorius,  22,  147-149,  *98-*100,  *106, 
174,  177,  217,  218,  220,  221,  282, 
283,  410. 

septi,  *76,  *114,  166,  *123. 
opticus,  7,  *25,  *37,  *69,  120,  124,  *74- 
*76,  126,  *79-*82,  133,  *84,  *86, 
138,  139,  *91-*93,  142,  143,  *95, 
*99.  *100,  *108,  *109,  "110,  *114, 
*122,   154,   158,  244,   *165,   259- 
261,  *169,  *173,  *175-*180,  279, 
282-290,   *183,   294,   *193,   *195, 
*198,  *237,  409,  410. 
pneumogastric,  motor,  87. 
nucleo-cerebellaris,  109. 
vago-cerebellaris,  86,  *46,  *52-*54,  108. 
vago-tectalis,  86,  *52-*54,  108. 
trigeminal,  bulbo-spinalis,  *47,  *52,  *53, 

364,  *234,  394,  *251. 
central,  *49,  *65,  *251. 
cortical,  408. 
ex  lobo.  97,  *54. 

mesencephalic.  *251,  *252,  396,  397. 
nucleo-cerebellaris,  109. 


GENERAL   INDEX. 


445 


Tract,  nerve,  trigeminal   quinto-cerebellaris, 

*53,  108,  *71,  327,  328. 
tectalis,  *51,  *53. 
thalamic,  *87,  *251. 
secondary,  394. 

nucleo-cerebellar,  106,  326,  *212. 
occipito-frontalis,  177,  *121,  *186. 
mesencephalicus,  174,  *121. 
tectalis,  *84. 

olfacto-habenularis,  130,  *99,  *100,  *120. 
order,  first  or  second,  23,  24,  "14,  72,  81, 

*227,  352. 

pallii,  *90,  *93,  145,  "122,  246,  256. 
peduncularis  transversa,  294. 
septo-mesencephalicus,  *76,  *84,  *99,  *101, 
*104,  166,  *114,  *115,  *120,  174, 
175. 

speech,  245,  246,  402-407. 
strio-hypothalamicus,  156. 
olfactorius,  *141,  *143,  *144. 
thalamicus,  *69,  "70,  *72,  *75,  *80,  *81, 
132,  134,  *83,  *84,  136,  *86,  *87, 
*89-*93,  143,  144,  *95,  *98,  *99. 
*102,  *104,  156,  157,  *120,  *122, 
256,  257,  274. 
dorsalis,  *82. 
tecto-bulbaris,  8,  72,  81,  99,  113,  *64,  *65, 

116,  "67,  118,  *88,  *91,  "92. 
spinalis,  3,  *30,  72,  *40c,  *41,  81,  *43,  *46. 
*52,  *54,  98,  *64,  99,   113,  *65, 
116,  *67,  118,  *71,  *72,  *88,  *91, 
*92. 

thalamicus,  120. 
thalamo-spinalis,  *41,  81. 
tegmentalis.  10,  272,  315,  381. 

central    of    Bechterew,    381,    *243,    383, 

*244,  *245,  *248. 

tegmento-cerebellaris,  *59,  *60,  107,  *71, 
122,  *83,  *84,  *92,  137,  272, 
299. 

mamillaris,  *177,  *191. 
temporal  to  pons,  254. 

to  thalamus,  278,  279. 

temporo-occipitalis  ad  pontem,  252,  *163. 
thalamencephalo-cerebellaris,   107. 
thalamo-bulbaris,  134,  136,  272.  *201o. 
cerebellaris,  *58. 

mamillaris  (bundle  of  Vicq  d'Azyr),  *72, 
132,  *83,  *120,  268,  "174,  "178, 
274,  275. 
oblongatal,  272. 
spinalis,  *71,  134,  136. 
tectalis,  "72,  132,  *83,  "84,  294. 
tegmentalis,  277. 
transversus  taeniae,  *100. 
Tract-cells,  cord,  358. 
Transmission  of  impulses,  23,  33,  39,  116. 
Trapezium,  pons,  387,  388,  "247,  *248. 
Trapezius,  spinal  center,  336. 
Tremor,  unilateral,  270. 
Triceps,  spinal  center,  336. 
Trigeminus,  see  nerve,  trigeminal. 
Trochlearis,  see  nerve,  trochlear. 
Truncus,  cortical  center,  *148,  *149. 
Tube,  epiphyseal,  127. 


Tuber  cinereum,  *20,  128,  187,  188,  190,  "144, 
*174,  *178,  "181,  280,  "195,  409. 
taenise,  *100,  152. 

valvute  cerebelli,  316,  "203,  317,  319. 
vermis,  316. 
Tuberculum  acusticum,  *47,  *49,  93,  *54,  97, 

385,  387,  388,  "247. 
thalami  anterius,  "125,  188,  259,  274. 
j  Tubule,  epithelial,  of  hypophysis,  280,  281. 
Tumor,  brain,  309,  329,  330. 
cerebellum,  329-331. 
medulla  and  pons,  402-405. 

Uncus,  *133,  197,  *135,  "176;    see  also  gyrus 

uncinatus. 
Uvula  cerebelli,  *204,  317,  319. 

Vagus,  see  nerve,  pneumogastric. 

Valvula  cerebelli,  *18,  *39,  *44,  105,  "60,  "68, 

"76,  *85,  "86,  *95,  "114. 
Velum  chorioideum,  "18,  5z,  145. 
interpositum,  201. 

medullare  anticum,  101,  "56,  "60,  108,  121, 
*86,  "95,  "144,  "182,  »201b,  SIS- 
SIS,  "202,  204,  317,  318,  323,  328, 
"236,  372,  374,  "253,  399,  401. 
posticum,  121,  314,  319,  "236,  372. 
Ventricle  of  brain,  50,  53,  54  (ventriculus). 
fourth  (fossa  rhomboidalis),  21,  56,  75,  "37, 
"39,  78,  86,  87,  89,  94,  "53,  "54, 
101,    127,    "86,    "87,    "92,    "95, 
"182,  310,  315,   319,   "210,  324, 
328,    363,    372-374,    "239,    376, 
*243,  388,  390-392,  399. 
lateral,  52,  "22,  53,  "79,  153,  156,  159,  162, 
"118,    183-187,   "125,   "127,   190, 
198,   199,   "134,   200,   210,   "141, 
213,    218,    220,    "154,    240-242, 
•161,   249,   "162,   264-268,   "171, 
"172,    278,    279,    291-293,    "188, 
"189. 
horn,  anterior,  266. 

inferior,  or  middle,  "154,  249,  278,  291- 

293. 

posterior,  198,  292,  293. 
lobe,  olfactory,  "94,  "142. 
midbrain,  "64,  121,  "73,  "75. 
septi  pellucidi,  186,  "125,  190,  266. 
third  (medius),  52,  "21,  "22,  "75,  127,  138, 
"87,  "102,  "106,  "118.  186,  187, 
190,    197,    "158,    258-260,    "168, 
"169,  267,  268,   "176,  278,  280, 
"182,  289,  294,  295,   "196,  303, 
"197,  "236. 
Verga,  186. 

Vermis  cerebelli,  102,  105,  108,  315-318,  "206, 
322-324,  "211,  326,  327,  330,  349, 
350,  379,  "241,  "244,  "245,  391, 
"252. 

Vertigo,  330. 
Vesicles,  primary,  of  brain,  49,  50,  "21,  159, 

187. 

Vestibule  of  ear,  91. 

Viscera,  innervation,  24,  "17,  67,  68,  70,  84, 
86,  304,  334,  356. 


446 


GENERAL    INDEX. 


Vision,  cortical  center,  *148,  226;    see  also 

sight. 

disturbance  of,  330,  410. 
physiology,  comparative,  176. 


Waller,  law  of,  6,  7,  333. 

Weight,  of  brain,  206,  207. 

Word-blindness,  240. 

Worm  of  cerebellum,  *182;    see  vermis. 

Wrist,  cortical  center,  *148. 


Zona  granulosa,  bulb,  olfactory,  213. 


Zona   granulosa.   cortex   cerebelli,   319,   320, 

*207,  *208,  328,  329. 
incerta,  regio  subthalamica,  276,  "178. 
marginalis,  cord,  *223,  *225,  350,  355. 
mixed,  antero-lateral,  cord,  350,  355. 
molecularis  cerebelli,   110,   319,  320,   *207, 

328. 

motor,  of  extremities,  251. 
of  His,  84. 
radicular,  *225,  *226. 

anterior,  350,  351,  355,  356. 
spongiosa,  355. 
terminalis,  355. 
Zone  of  decussation,  cerebellum,  *210. 


University  of  California 

SOUTHERN  REGIONAL  LIBRARY  FACILITY 

405  Hilgard  Avenue,  Los  Angeles,  CA  90024-1388 

Return  this  material  to  the  library 

from  which  it  wss  borrowed. 


A  000510431  o 


.  - 


WL101 
E23a 
1899 
Edinger . 

The  anatomy  of  the  central 
nervous  system  of  man 

DATE  ISSUED  TO 


WL101 
E23a 
1899 
Edinger . 

The  anatomy  of  the  central 
nervous  system  of  man 


UCI  CCM  LIBRARY 


